Production of oligodendrocytes from placenta-derived stem cells

ABSTRACT

The present invention provides methods and compositions for the production of glial cells and oligodendrocytes from placenta stem cells. The invention further provides for the use of these glia and oligodendrocytes in the treatment of, and intervention in, for example, trauma, ischemia and degenerative disorders of the central nervous system (CNS), particularly in the treatment of demyelinating diseases such as multiple sclerosis.

1. FIELD OF THE INVENTION

The present invention provides methods and compositions for the production of glial cells and oligodendrocytes from placenta-derived stem cells (referred to hereafter as PDSCs). The invention further provides for the use of these glia and oligodendrocytes in the treatment of, and intervention in, for example, trauma, ischemia and degenerative disorders of the central nervous system (CNS).

2. BACKGROUND OF THE INVENTION

Embryonic stem cells capable of generating CNS glia can promote functional recovery after trauma to the spinal cord, and have potential for repair in demyelinating and dysmyelinating diseases such as multiple sclerosis. However, the use of embryonic stem cells for clinical therapy raises ethical concerns that cannot be easily addressed.

Somatic stem cells have also been proposed for therapeutic applications. For example, in animal models of cell replenishment therapy. The therapeutic potential of grafted stem cells can only be translated to clinical use if an ethically acceptable source of autologous stem cells is available, and if control of self renewal and fate decisions that program stem cell maturation into specific cell types is achieved.

Neurodegenerative disorders increasingly account for significant morbidity and mortality. Destruction of myelin underlies the most common neurological disorder in young adults, multiple sclerosis, and myelin affects repair after traumatic spinal cord injury, preventing regeneration of damaged neuronal axons and affecting electrical conduction in proximal, undamaged axons. Replacement of oligodendrocytes is thus a significant clinical goal. While oligodendrocytes are obtainable from neural stem cells, such stem cells are difficult to obtain.

3. SUMMARY OF THE INVENTION

The present invention provides methods and compositions for the production of oligodendrocytes from placenta derived stem cells, and methods of using such oligodendrocytes to treat diseases, disorders or conditions, such as those involving trauma, ischemia, or systemic disorders of the central nervous system. For example, in one aspect, the present invention relates to use of oligodendrocytes produced from placenta-derived stem cells in the treatment of diseases, disorders or conditions associated with abnormal myelination. In one embodiment, the invention provides a method of producing an oligodendrocyte, comprising culturing a placenta-derived stem cell under conditions and for a time sufficient for said stem cell to exhibit a characteristic of an oligodendrocyte. In a specific embodiment, said characteristic is the production of myelin oligodendrocyte specific protein or expression of a gene encoding myelin oligodendrocyte specific protein. In another specific embodiment, said culturing comprises contacting said stem cell with isobutylmethylxanthine (IBMX). In another embodiment, the invention provides an oligodendrocyte produced by differentiation of a placenta derived stem cell. The invention also provides a method of treating a subject having a disease, disorder or condition associated with abnormal myelination, comprising introducing such an oligodendrocyte of into said subject. In a more specific embodiment, the disease, disorder or condition is multiple sclerosis.

4. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1: Oligodendrocyte progenitor cell maturation (McMorris & McKinnon, Brain Pathology 6:313-329 (1996)). The temporal appearance of antigens marks progression from migratory “early” (O2A) progenitors to non-migratory “late” (O4, pro-OLblasts) and postmitotic OLs. Maturation can be reversibly inhibited (ζ), or reversed (7) with the indicated factors. Monoclonal antibodies and target antigens are outlined in Table 1.

FIG. 2: Human placental stem cells. Left: placental stem cell colony formed in primary culture. Right: placental stem cells treated with isobutylmethylxanthine (IBMX, a nonspecific inhibitor of phosphodiesterases that also possesses adenosine agonist activity); immunostaining shows the presence of neural lineage markers including neural stem cell markers (vimentin, GFAP, nestin), as well as markers for both neuronal (neurofilament, neuron specific enolase) and glial (myelin oligodendrocyte specific protein (MOSP)) lineage progression.

5. DETAILED DESCRIPTION OF THE INVENTION

5.1 Production of Oligodendrocytes

The present invention provides methods and compositions for the production of oligodendrocytes from placenta-derived cells, particularly placental stem cells, also referred to as placenta-derived stem cells (PDSCs). Stem cells may be obtained from a mammalian placenta by perfusion (see, e.g., Hariri, U.S. Application Publication Nos. 2002/0123141 and 2003/0032179, which are hereby incorporated herein in their entireties. Stem cells may also be obtained from placenta by disruption (e.g., maceration) of a placenta or part thereof (see., e.g., Section 6.2). Cells displaying oligodendrocyte characteristics may be obtained from placenta derived stem cells. These cells are useful in the treatment of diseases, disorders or conditions associated with, for example, demyelination or dysmyelination, such as multiple sclerosis.

In one embodiment, differentiable cells, such as stem cells, may be obtained from the placenta as follows. Primary cultures of mononuclear cells (MNCs) are isolated from placentas, e.g., human placenta perfusates. The placentas are obtained following birth of full-term infants under informed consent of the donors. Briefly, umbilical vessels are cannulated then connected to a flow-controlled circuit, and the placenta is perfused at, e.g., 1 mL/min (room temperature, up to 24 hours) with Dulbecco's modified Eagle's medium (DMEM, Gibco/BRL) containing high glucose, 1% heparin and penicillin/streptomycin. Placenta perfusate (750 mL) is then pooled, centrifuged, and the cell pellet resuspended in PBS containing 1% fetal calf serum (FBS) then separated by differential gradient density centrifugation through Lymphoprep™ (Gibco/BRL). The buffy-coat interface containing mononucleated cells including adherent PDSCs are recovered, resuspended in DMEM/10% FBS, plated on fibronectin-coated (Sigma) Falcon plates and incubated at 37<C with 5% humidified CO₂. After a 24-hour incubation the nonadherent cells are discarded and the adherent cells are maintained and expanded in fresh culture media; individual cell colonies develop between 10 and 18 days and are expanded as PDSC lines.

Human placenta-derived stem cells (PDSCs) display fibroblast-like morphology in culture (FIG. 2 a) and are HLA-class I positive. Using FACS analysis these cells do not express the hematopoietic markers CD34 or CD45. However, they do express the multipotential surface markers CD10 (CALLA), CD29 (β₁ integrin), CD54 (ICAM-1), CD90 (Thy-1) as well as SH2 and SH3. Under standard growth conditions the doubling time for PDSCs is 18 to 36 hours, and the cells maintain this phenotype for greater than 40 population doublings in vitro.

A number of studies have described neural differentiation of stem cells in vitro and in vivo, including embryonic, hematopoietic and bone marrow stromal cells (Glaser et al., FASEB J. 2005 19(1):112-4 (2005); Rogister et al., Cellular Neuroscience 14:287-300 (1999); Rao and MayerProschel, Dev. Biol. 188:48-63 (1997); Anderson, Neuron 30:19-35 (2001); Rao, Stem Cells and Development 13:452-455 (2004); Hermanson et al., Nature 419:934-939 (2002); Johe et al., Genes Dev. 10:3129-3140 (1996)).

Neural differentiation in vitro can be promoted using agents that elevate intracellular cAMP. To determine whether cells derived from human placenta are capable of generating neural lineages, their was examined under similar conditions in vitro. Monolayer PDSCs were harvested (0.25% trypsin, 1 mM EDTA) then replated at (5×10³/mL) in culture medium containing 0.5 mM IBMX (Sigma), and morphologic changes were monitored after 24-72 hours by phase contrast microscopy, immunofluorescence and flow cytometry. After 3 days in culture approximately 50% of cells had a neural-like morphology with long processes and a pronounced spherical cell soma, while control cultures remained undifferentiated. IBMX-treated cultures also displayed immunoreactivity for a number of neuroepithelial lineage markers including neural progenitor markers (nestin, vimentin, GFAP), neuronal markers (enolase, neurofilament), and cells that exhibited glia markers (MOSP) (FIG. 2). To determine the temporal profile of neural antigen expression flow cytometry was performed on both treated and untreated PDSCs. A pronounced shift in antigenic expression was apparent after day 1 with IBMX for all markers tested, with no shift in untreated cells. Thus the changes observed under these induction conditions reflect the rapid acquisition of antigenic markers, consistent with neural differentiation rather than a selective enrichment or survival.

Placenta-derived stem cells may be differentiated to oligodendrocytes by culturing in culture medium comprising IBMX, neural stem cell maturation factors (e.g., EGF, FGF), and/or oligodendrocyte progenitor cell mitogens (e.g., FGF, PDGF). Oligodendrocytes can be produced from placenta derived stem cells as described above, and maintained or cultured as described in Section 6.1. Oligodendrocyte differentiation can be assessed using immunohistochemistry and PCR as described in Section 6.3 and flow cytometry as described in Section 6.5. Oligodendrocyte proliferation, migration, and survival can be assessed as described in Section 6.4.

5.2 Placental Stem Cells and Placental Stem Cell Populations

The methods of immunosuppression of the present invention use placental stem cells, that is, stem cells obtainable from a placenta or part thereof, that (1) adhere to a tissue culture substrate; (2) have the capacity to differentiate into non-placental cell types; and (3) have, in sufficient numbers, the capacity to detectably suppress an immune function, e.g., proliferation of CD4⁺ and/or CD8⁺ stem cells in a mixed lymphocyte reaction assay. Placental stem cells are not derived from blood, e.g., placental blood or umbilical cord blood. The placental stem cells used in the methods and compositions of the present invention have the capacity, and are selected for their capacity, to suppress the immune system of an individual.

Placental stem cells can be either fetal or maternal in origin (that is, can have the genotype of either the mother or fetus). Populations of placental stem cells, or populations of cells comprising placental stem cells, can comprise placental stem cells that are solely fetal or maternal in origin, or can comprise a mixed population of placental stem cells of both fetal and maternal origin. The placental stem cells, and populations of cells comprising the placental stem cells, can be identified and selected by the morphological, marker, and culture characteristics discussed below.

5.2.1 Physical and Morphological Characteristics

The placental stem cells used in the present invention, when cultured in primary cultures or in cell culture, adhere to the tissue culture substrate, e.g., tissue culture container surface (e.g., tissue culture plastic). Placental stem cells in culture assume a generally fibroblastoid, stellate appearance, with a number of cyotplasmic processes extending from the central cell body. The placental stem cells are, however, morphologically differentiable from fibroblasts cultured under the same conditions, as the placental stem cells exhibit a greater number of such processes than do fibroblasts. Morphologically, placental stem cells are also differentiable from hematopoietic stem cells, which generally assume a more rounded, or cobblestone, morphology in culture.

5.2.2 Cell Surface, Molecular and Genetic Markers

Placental stem cells, and populations of placental stem cells, useful in the methods and compositions of the present invention, express a plurality of markers that can be used to identify and/or isolate the stem cells, or populations of cells that comprise the stem cells. The placental stem cells, and stem cell populations of the invention (that is, two or more placental stem cells) include stem cells and stem cell-containing cell populations obtained directly from the placenta, or any part thereof (e.g., amnion, chorion, placental cotyledons, and the like). Placental stem cell populations also includes populations of (that is, two or more) placental stem cells in culture, and a population in a container, e.g., a bag. Placental stem cells are not, however, trophoblasts.

Placental stem cells generally express the markers CD73, CD105, CD200, HLA-G, and/or OCT-4, and do not express CD34, CD38, or CD45. Placental stem cells can also express HLA-ABC (MHC-1) and HLA-DR. These markers can be used to identify placental stem cells, and to distinguish placental stem cells from other stem cell types. Because the placental stem cells can express CD73 and CD105, they can have mesenchymal stem cell-like characteristics. However, because the placental stem cells can express CD200 and HLA-G, a fetal-specific marker, they can be distinguished from mesenchymal stem cells, e.g., bone marrow-derived mesenchymal stem cells, which express neither CD200 nor HLA-G. In the same manner, the lack of expression of CD34, CD38 and/or CD45 identifies the placental stem cells as non-hematopoietic stem cells.

In one embodiment, the invention provides an isolated cell population comprising a plurality of immunosuppressive placental stem cells that are CD200⁺, HLA-G⁺, wherein said plurality detectably suppresses T cell proliferation in a mixed lymphocyte reaction (MLR) assay. In a specific embodiment of the isolated populations, said stem cells are also CD73⁺ and CD105⁺. In another specific embodiment, said stem cells are also CD34⁻, CD38⁻ or CD45⁻. In a more specific embodiment, said stem cells are also CD34⁻, CD38⁻, CD45⁻, CD73⁺ and CD105⁺. In another embodiment, said isolated population produces one or more embryoid-like bodies when cultured under conditions that allow the formation of embryoid-like bodies.

In another embodiment, the invention provides an isolated cell population comprising a plurality of immunosuppressive placental stem cells that are CD73⁺, CD105⁺, CD200⁺, wherein said plurality detectably suppress T cell proliferation in a mixed lymphocyte reaction (MLR) assay. In a specific embodiment of said populations, said stem cells are HLA-G⁺. In another specific embodiment, said stem cells are CD34⁻, CD38⁻ or CD45⁻. In another specific embodiment, said stem cells are CD34⁻, CD38⁻ and CD45⁻. In a more specific embodiment, said stem cells are CD34⁻, CD38⁻, CD45⁻, and HLA-G⁺. In another specific embodiment, said population of cells produces one or more embryoid-like bodies when cultured under conditions that allow the formation of embryoid-like bodies.

The invention also provides an isolated cell population comprising a plurality of immunosuppressive placental stem cells that are CD200⁺, OCT-4⁺, wherein said plurality detectably suppresses T cell proliferation in a mixed lymphocyte reaction (MLR) assay. In a specific embodiment, said stem cells are CD73⁺ and CD105⁺. In another specific embodiment, said stem cells are HLA-G⁺. In another specific embodiment, said stem cells are CD34⁻, CD38⁻ and CD45⁻. In a more specific embodiment, said stem cells are CD34⁻, CD38⁻, CD45⁻, CD73⁺, CD105⁺ and HLA-G⁺. In another specific embodiment, the population produces one or more embryoid-like bodies when cultured under conditions that allow the formation of embryoid-like bodies.

The invention also provides an isolated cell population comprising a plurality of immunosuppressive placental stem cells that are CD73⁺, CD105⁺ and HLA-G⁺, wherein said plurality detectably suppresses T cell proliferation in a mixed lymphocyte reaction (MLR) assay. In a specific embodiment of the above plurality, said stem cells are also CD34⁻, CD38⁻ or CD45⁻. In another specific embodiment, said stem cells are also CD34⁻, CD38⁻ and CD45⁻. In another specific embodiment, said stem cells are also OCT-4⁺. In another specific embodiment, said stem cells are also CD200⁺. In a more specific embodiment, said stem cells are also CD34⁻, CD38⁻, CD45⁻, OCT-4⁺ and CD200⁺.

The invention also provides an isolated cell population comprising a plurality of immunosuppressive placental stem cells that are CD73⁺, CD105⁺ stem cells, wherein said plurality forms one or more embryoid-like bodies under conditions that allow formation of embryoid-like bodies, and wherein said plurality detectably suppresses T cell proliferation in a mixed lymphocyte reaction (MLR) assay. In a specific embodiment, said stem cells are also CD34⁻, CD38⁻ or CD45⁻. In another specific embodiment, said stem cells are also CD34⁻, CD38⁻ and CD45⁻. In another specific embodiment, said stem cells are also OCT-4⁺. In a more specific embodiment, said stem cells are also OCT-4⁺, CD34⁻, CD38⁻ and CD45⁻.

The invention also provides an isolated cell population comprising a plurality of immunosuppressive placental stem cells that are OCT-4⁺ stem cells, wherein said population forms one or more embryoid-like bodies when cultured under conditions that allow the formation of embryoid-like bodies, and wherein said plurality detectably suppresses T cell proliferation in a mixed lymphocyte reaction (MLR) assay. In various embodiments, at least 10%, at least 20%, at least 30%, at least 40%, at least 50% at least 60%, at least 70%, at least 80%, at least 90%, or at least 95% of said isolated placental cells are OCT4⁺ stem cells. In a specific embodiment of the above populations, said stem cells are CD73⁺ and CD105⁺. In another specific embodiment, said stem cells are CD34⁻, CD38⁻, or CD45⁻. In another specific embodiment, said stem cells are CD200⁺. In a more specific embodiment, said stem cells are CD73⁺, CD105⁺, CD200⁺, CD34⁻, CD38⁻, and CD45⁻. In another specific embodiment, said population has been expanded, for example, passaged at least once, at least three times, at least five times, at least 10 times, at least 15 times, or at least 20 times.

In another embodiment, the invention provides an isolated cell population comprising a plurality of immunosuppressive placental stem cells that are CD29⁺, CD44⁺, CD73⁺, CD90⁺, CD105⁺, CD200⁺, CD34⁻ and CD133⁻.

In a specific embodiment of the above-mentioned placental stem cells, the placental stem cells constitutively secrete IL-6, IL-8 and monocyte chemoattractant protein (MCP-1).

Each of the above-referenced pluralities of placental stem cells can comprise placental stem cells obtained and isolated directly from a mammalian placenta, or placental stem cells that have been cultured and passaged at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 25, 30 or more times, or a combination thereof.

The immunosuppressive pluralities of placental stem cells described above can comprise about, at least, or no more than, 1×10⁵, 5×10⁵, 1×10⁶, 5×10⁶, 1×10⁷, 5×10⁷, 1×10⁸, 5×10⁸, 1×10⁹, 5×10⁹, 1×10¹⁰, 5×10¹⁰, 1×10¹¹ or more placental stem cells.

5.2.3 Selecting and Producing Placental Stem Cell Populations

In another embodiment, the invention also provides a method of selecting a plurality of immunosuppressive placental stem cells from a plurality of placental cells, comprising selecting a population of placental cells wherein at least 10%, at least 20%, at least 30%, at least 40%, at least 50% at least 60%, at least 70%, at least 80%, at least 90%, or at least 95% of said cells are CD200⁺, HLA-G⁺ placental stem cells, and wherein said placental stem cells detectably suppresses T cell proliferation in a mixed lymphocyte reaction (MLR) assay. In a specific embodiment, said selecting comprises selecting stem cells that are also CD73⁺ and CD105⁺. In another specific embodiment, said selecting comprises selecting stem cells that are also CD34⁻, CD38⁻ or CD45⁻. In another specific embodiment, said selecting comprises selecting placental stem cells that are also CD34⁻, CD38⁻, CD45⁻, CD73⁺ and CD105⁺. In another specific embodiment, said selecting also comprises selecting a plurality of placental stem cells that forms one or more embryoid-like bodies when cultured under conditions that allow the formation of embryoid-like bodies.

In another embodiment, the invention also provides a method of selecting a plurality of immunosuppressive placental stem cells from a plurality of placental cells, comprising selecting a plurality of placental cells wherein at least 10%, at least 20%, at least 30%, at least 40%, at least 50% at least 60%, at least 70%, at least 80%, at least 90%, or at least 95% of said cells are CD73⁺, CD105⁺, CD200⁺ placental stem cells, and wherein said placental stem cells detectably suppresses T cell proliferation in a mixed lymphocyte reaction (MLR) assay. In a specific embodiment, said selecting comprises selecting stem cells that are also HLA-G⁺. In another specific embodiment, said selecting comprises selecting placental stem cells that are also CD34⁻, CD38⁻ or CD45⁻. In another specific embodiment, said selecting comprises selecting placental stem cells that are also CD34⁻, CD38⁻ and CD45⁻. In another specific embodiment, said selecting comprises selecting placental stem cells that are also CD34⁻, CD38⁻, CD45⁻, and HLA-G⁺. In another specific embodiment, said selecting additionally comprises selecting a population of placental cells that produces one or more embryoid-like bodies when the population is cultured under conditions that allow the formation of embryoid-like bodies.

In another embodiment, the invention also provides a method of selecting a plurality of immunosuppressive placental stem cells from a plurality of placental cells, comprising selecting a plurality of placental cells wherein at least 10%, at least 20%, at least 30%, at least 40%, at least 50% at least 60%, at least 70%, at least 80%, at least 90%, or at least 95% of said cells are CD200⁺, OCT-4⁺ placental stem cells, and wherein said placental stem cells detectably suppresses T cell proliferation in a mixed lymphocyte reaction (MLR) assay. In a specific embodiment, said selecting comprises selecting placental stem cells that are also CD73⁺ and CD105⁺. In another specific embodiment, said selecting comprises selecting placental stem cells that are also HLA-G⁺. In another specific embodiment, said selecting comprises selecting placental stem cells that are also CD34⁻, CD38⁻ and CD45⁻. In another specific embodiment, said selecting comprises selecting placental stem cells that are also CD34⁻, CD38⁻, CD45⁻, CD73⁺, CD105⁺ and HLA-G⁺.

In another embodiment, the invention also provides a method of selecting a plurality of immunosuppressive placental stem cells from a plurality of placental cells, comprising selecting a plurality of placental cells wherein at least 10%, at least 20%, at least 30%, at least 40%, at least 50% at least 60%, at least 70%, at least 80%, at least 90%, or at least 95% of said cells are CD73⁺, CD105⁺ and HLA-G+placental stem cells, and wherein said placental stem cells detectably suppresses T cell proliferation in a mixed lymphocyte reaction (MLR) assay. In a specific embodiment, said selecting comprises selecting placental stem cells that are also CD34⁻, CD38⁻ or CD45⁻. In another specific embodiment, said selecting comprises selecting placental stem cells that are also CD34⁻, CD38⁻ and CD45⁻. In another specific embodiment, said selecting comprises selecting placental stem cells that are also CD200⁺. In another specific embodiment, said selecting comprises selecting placental stem cells that are also CD34⁻, CD38⁻, CD45⁻, OCT-4⁺ and CD200⁺.

In another embodiment, the invention also provides a method of selecting a plurality of immunosuppressive placental stem cells from a plurality of placental cells, comprising selecting a plurality of placental cells wherein at least 10%, at least 20%, at least 30%, at least 40%, at least 50% at least 60%, at least 70%, at least 80%, at least 90%, or at least 95% of said cells are CD73⁺, CD105⁺ placental stem cells, and wherein said plurality forms one or more embryoid-like bodies under conditions that allow formation of embryoid-like bodies. In a specific embodiment, said selecting comprises selecting placental stem cells that are also CD34⁻, CD38⁻ or CD45⁻. In another specific embodiment, said selecting comprises selecting placental stem cells that are also CD34⁻, CD38⁻ and CD45⁻. In another specific embodiment, said selecting comprises selecting placental stem cells that are also OCT-4⁺. In a more specific embodiment, said selecting comprises selecting placental stem cells that are also OCT-4⁺, CD34⁻, CD38⁻ and CD45⁻.

In another embodiment, the invention also provides a method of selecting a plurality of immunosuppressive placental stem cells from a plurality of placental cells, comprising selecting a plurality of placental cells wherein at least 10%, at least 20%, at least 30%, at least 40%, at least 50% at least 60%, at least 70%, at least 80%, at least 90%, or at least 95% of said isolated placental cells are OCT4⁺ stem cells, and wherein said plurality forms one or more embryoid-like bodies under conditions that allow formation of embryoid-like bodies. In a specific embodiment, said selecting comprises selecting placental stem cells that are also CD73⁺ and CD105⁺. In another specific embodiment, said selecting comprises selecting placental stem cells that are also CD34⁻, CD38⁻, or CD45⁻. In another specific embodiment, said selecting comprises selecting placental stem cells that are also CD200⁺. In a more specific embodiment, said selecting comprises selecting placental stem cells that are also CD73⁺, CD105⁺, CD200⁺, CD34⁻, CD38⁻, and CD45⁻.

The invention also provides methods of producing immunosuppressive populations, or pluralities, of placental stem cells. For example, the invention provides a method of producing a cell population, comprising selecting any of the pluralities of placental stem cells described above, and isolating the plurality of placental stem cells from other cells, e.g., other placental cells. In a specific embodiment, the invention provides a method of producing a cell population comprising selecting placental cells, wherein said placental cells (a) adhere to a substrate, (b) express CD200 and HLA-G, or express CD73, CD105, and CD200, or express CD200 and OCT-4, or express CD73, CD105, and HLA-G, or express CD73 and CD105 and facilitate the formation of one or more embryoid-like bodies in a population of placental cells that comprise the stem cell, when said population is cultured under conditions that allow formation of embryoid-like bodies, or express OCT-4 and facilitate the formation of one or more embryoid-like bodies in a population of placental cells that comprise the stem cell, when said population is cultured under conditions that allow formation of embryoid-like bodies; and (c) detectably suppress CD4⁺ or CD8⁺ T cell proliferation in an MLR (mixed lymphocyte reaction); and isolating said placental cells from other cells to form a cell population.

In a more specific embodiment, the invention provides a method of producing a cell population comprising selecting placental stem cells that (a) adhere to a substrate, (b) express CD200 and HLA-G, and (c) detectably suppress CD4⁺ or CD8⁺ T cell proliferation in an MLR (mixed lymphocyte reaction); and isolating said placental stem cells from other cells to form a cell population. In another specific embodiment, the invention provides a method of producing a cell population comprising selecting placental stem cells that (a) adhere to a substrate, (b) express CD73, CD105, and CD200, and (c) detectably suppress CD4⁺ or CD8⁺ T cell proliferation in an MLR; and isolating said placental stem cells from other cells to form a cell population. In another specific embodiment, the invention provides a method of producing a cell population comprising selecting placental stem cells that (a) adhere to a substrate, (b) express CD200 and OCT-4, and (c) detectably suppress CD4⁺ or CD8⁺ T cell proliferation in an MLR; and isolating said placental stem cells from other cells to form a cell population. In another specific embodiment, the invention provides a method of producing a cell population comprising selecting placental stem cells that (a) adhere to a substrate, (b) express CD73 and CD105, (c) form embryoid-like bodies when cultured under conditions allowing the formation of embryoid-like bodies, and (d) detectably suppress CD4⁺ or CD8⁺ T cell proliferation in an MLR; and isolating said placental stem cells from other cells to form a cell population. In another specific embodiment, the invention provides a method of producing a cell population comprising selecting placental stem cells that (a) adhere to a substrate, (b) express CD73, CD105, and HLA-G, and (c) detectably suppress CD4⁺ or CD8⁺ T cell proliferation in an MLR; and isolating said placental stem cells from other cells to form a cell population. A method of producing a cell population comprising selecting placental stem cells that (a) adhere to a substrate, (b) express OCT-4, (c) form embryoid-like bodies when cultured under conditions allowing the formation of embryoid-like bodies, and (d) detectably suppress CD4⁺ or CD8⁺ T cell proliferation in an MLR; and isolating said placental stem cells from other cells to form a cell population.

In a specific embodiment of the methods of producing an immunosuppressive placental stem cell population, said T cells and said placental cells are present in said MLR at a ratio of about 5:1. The placental cells used in the method can be derived from the whole placenta, or primarily from amnion, or amnion and chorion. In another specific embodiment, the placental cells suppress CD4⁺ or CD8⁺ T cell proliferation by at least 50%, at least 75%, at least 90%, or at least 95% in said MLR compared to an amount of T cell proliferation in said MLR in the absence of said placental cells. The method can additionally comprise the selection and/or production of a placental stem cell population capable of immunomodulation, e.g., suppression of the activity of, other immune cells, e.g., an activity of a natural killer (NK) cell.

5.2.4 Growth in Culture

The growth of the placental stem cells described herein, as for any mammalian cell, depends in part upon the particular medium selected for growth. Under optimum conditions, placental stem cells typically double in number in 3-5 days. During culture, the placental stem cells of the invention adhere to a substrate in culture, e.g. the surface of a tissue culture container (e.g., tissue culture dish plastic, fibronectin-coated plastic, and the like) and form a monolayer.

Populations of isolated placental cells that comprise the placental stem cells of the invention, when cultured under appropriate conditions, form embryoid-like bodies, that is, three-dimensional clusters of cells grow atop the adherent stem cell layer. Cells within the embryoid-like bodies express markers associated with very early stem cells, e.g., OCT-4, Nanog, SSEA3 and SSEA4. Cells within the embryoid-like bodies are typically not adherent to the culture substrate, as are the placental stem cells described herein, but remain attached to the adherent cells during culture. Embryoid-like body cells are dependent upon the adherent placental stem cells for viability, as embryoid-like bodies do not form in the absence of the adherent stem cells. The adherent placental stem cells thus facilitate the growth of one or more embryoid-like bodies in a population of placental cells that comprise the adherent placental stem cells. Without wishing to be bound by theory, the cells of the embryoid-like bodies are thought to grow on the adherent placental stem cells much as embryonic stem cells grow on a feeder layer of cells. Mesenchymal stem cells, e.g., bone marrow-derived mesenchymal stem cells, do not develop embryoid-like bodies in culture.

5.2.5 Differentiation

The placental stem cells, useful in the methods of the present invention, are differentiable into different committed cell lineages. For example, the placental stem cells can be differentiated into cells of an adipogenic, chondrogenic, neurogenic, or osteogenic lineage. Such differentiation can be accomplished by any method known in the art for differentiating, e.g., bone marrow-derived mesenchymal stem cells into similar cell lineages.

5.3 Methods of Obtaining Placental Stem Cells

5.3.1 Stem Cell Collection Composition

The present invention further provides methods of collecting and isolating placental stem cells. Generally, stem cells are obtained from a mammalian placenta using a physiologically-acceptable solution, e.g., a stem cell collection composition. A stem cell collection composition is described in detail in related U.S. Provisional Application No. 60/754,969, entitled “Improved Composition for Collecting and Preserving Placental Stem Cells and Methods of Using the Composition” filed on Dec. 29, 2005.

The stem cell collection composition can comprise any physiologically-acceptable solution suitable for the collection and/or culture of stem cells, for example, a saline solution (e.g., phosphate-buffered saline, Kreb's solution, modified Kreb's solution, Eagle's solution, 0.9% NaCl. etc.), a culture medium (e.g., DMEM, H.DMEM, etc.), and the like.

The stem cell collection composition can comprise one or more components that tend to preserve placental stem cells, that is, prevent the placental stem cells from dying, or delay the death of the placental stem cells, reduce the number of placental stem cells in a population of cells that die, or the like, from the time of collection to the time of culturing. Such components can be, e.g., an apoptosis inhibitor (e.g., a caspase inhibitor or JNK inhibitor); a vasodilator (e.g., magnesium sulfate, an antihypertensive drug, atrial natriuretic peptide (ANP), adrenocorticotropin, corticotropin-releasing hormone, sodium nitroprusside, hydralazine, adenosine triphosphate, adenosine, indomethacin or magnesium sulfate, a phosphodiesterase inhibitor, etc.); a necrosis inhibitor (e.g., 2-(1H-Indol-3-yl)-3-pentylaminomaleimide, pyrrolidine dithiocarbamate, or clonazepam); a TNF-α inhibitor; and/or an oxygen-carrying perfluorocarbon (e.g., perfluorooctyl bromide, perfluorodecyl bromide, etc.).

The stem cell collection composition can comprise one or more tissue-degrading enzymes, e.g., a metalloprotease, a serine protease, a neutral protease, an RNase, or a DNase, or the like. Such enzymes include, but are not limited to, collagenases (e.g., collagenase I, II, III or IV, a collagenase from Clostridium histolyticum, etc.); dispase, thermolysin, elastase, trypsin, LIBERASE, hyaluronidase, and the like.

The stem cell collection composition can comprise a bacteriocidally or bacteriostatically effective amount of an antibiotic. In certain non-limiting embodiments, the antibiotic is a macrolide (e.g., tobramycin), a cephalosporin (e.g., cephalexin, cephradine, cefuroxime, cefprozil, cefaclor, cefixime or cefadroxil), a clarithromycin, an erythromycin, a penicillin (e.g., penicillin V) or a quinolone (e.g., ofloxacin, ciprofloxacin or norfloxacin), a tetracycline, a streptomycin, etc. In a particular embodiment, the antibiotic is active against Gram(+) and/or Gram(−) bacteria, e.g., Pseudomonas aeruginosa, Staphylococcus aureus, and the like.

The stem cell collection composition can also comprise one or more of the following compounds: adenosine (about 1 mM to about 50 mM); D-glucose (about 20 mM to about 100 mM); magnesium ions (about 1 mM to about 50 mM); a macromolecule of molecular weight greater than 20,000 daltons, in one embodiment, present in an amount sufficient to maintain endothelial integrity and cellular viability (e.g., a synthetic or naturally occurring colloid, a polysaccharide such as dextran or a polyethylene glycol present at about 25 g/l to about 100 g/l, or about 40 g/l to about 60 g/l); an antioxidant (e.g., butylated hydroxyanisole, butylated hydroxytoluene, glutathione, vitamin C or vitamin E present at about 25 μM to about 100 μM); a reducing agent (e.g., N-acetylcysteine present at about 0.1 mM to about 5 mM); an agent that prevents calcium entry into cells (e.g., verapamil present at about 2 μM to about 25 μM); nitroglycerin (e.g., about 0.05 g/L to about 0.2 g/L); an anticoagulant, in one embodiment, present in an amount sufficient to help prevent clotting of residual blood (e.g., heparin or hirudin present at a concentration of about 1000 units/l to about 100,000 units/l); or an amiloride containing compound (e.g., amiloride, ethyl isopropyl amiloride, hexamethylene amiloride, dimethyl amiloride or isobutyl amiloride present at about 1.0 μM to about 5 μM).

5.3.2 Collection and Handling of Placenta

Generally, a human placenta is recovered shortly after its expulsion after birth. In a preferred embodiment, the placenta is recovered from a patient after informed consent and after a complete medical history of the patient is taken and is associated with the placenta. Preferably, the medical history continues after delivery. Such a medical history can be used to coordinate subsequent use of the placenta or the stem cells harvested therefrom. For example, human placental stem cells can be used, in light of the medical history, for personalized medicine for the infant associated with the placenta, or for parents, siblings or other relatives of the infant.

Prior to recovery of placental stem cells, the umbilical cord blood and placental blood are removed. In certain embodiments, after delivery, the cord blood in the placenta is recovered. The placenta can be subjected to a conventional cord blood recovery process. Typically a needle or cannula is used, with the aid of gravity, to exsanguinate the placenta (see, e.g., Anderson, U.S. Pat. No. 5,372,581; Hessel et al., U.S. Pat. No. 5,415,665). The needle or cannula is usually placed in the umbilical vein and the placenta can be gently massaged to aid in draining cord blood from the placenta. Such cord blood recovery may be performed commercially, e.g., LifeBank Inc., Cedar Knolls, N.J., ViaCord, Cord Blood Registry and Cryocell. Preferably, the placenta is gravity drained without further manipulation so as to minimize tissue disruption during cord blood recovery.

Typically, a placenta is transported from the delivery or birthing room to another location, e.g., a laboratory, for recovery of cord blood and collection of stem cells by, e.g., perfusion or tissue dissociation. The placenta is preferably transported in a sterile, thermally insulated transport device (maintaining the temperature of the placenta between 20-28° C.), for example, by placing the placenta, with clamped proximal umbilical cord, in a sterile zip-lock plastic bag, which is then placed in an insulated container. In another embodiment, the placenta is transported in a cord blood collection kit substantially as described in pending U.S. patent application Ser. No. 11/230,760, filed Sep. 19, 2005. Preferably, the placenta is delivered to the laboratory four to twenty-four hours following delivery. In certain embodiments, the proximal umbilical cord is clamped, preferably within 4-5 cm (centimeter) of the insertion into the placental disc prior to cord blood recovery. In other embodiments, the proximal umbilical cord is clamped after cord blood recovery but prior to further processing of the placenta.

The placenta, prior to stem cell collection, can be stored under sterile conditions and at either room temperature or at a temperature of 5 to 25° C. (centigrade). The placenta may be stored for a period of longer than forty eight hours, and preferably for a period of four to twenty-four hours prior to perfusing the placenta to remove any residual cord blood. The placenta is preferably stored in an anticoagulant solution at a temperature of 5 to 25° C. (centigrade). Suitable anticoagulant solutions are well known in the art. For example, a solution of heparin or warfarin sodium can be used. In a preferred embodiment, the anticoagulant solution comprises a solution of heparin (e.g., 1% w/w in 1:1000 solution). The exsanguinated placenta is preferably stored for no more than 36 hours before placental stem cells are collected.

The mammalian placenta or a part thereof, once collected and prepared generally as above, can be treated in any art-known manner, e.g., can be perfused or disrupted, e.g., digested with one or more tissue-disrupting enzymes, to obtain stem cells.

5.3.3 Physical Disruption and Enzymatic Digestion of Placental Tissue

In one embodiment, stem cells are collected from a mammalian placenta by physical disruption, e.g., enzymatic digestion, of the organ. For example, the placenta, or a portion thereof, may be, e.g., crushed, sheared, minced, diced, chopped, macerated or the like, while in contact with the stem cell collection composition of the invention, and the tissue subsequently digested with one or more enzymes. The placenta, or a portion thereof, may also be physically disrupted and digested with one or more enzymes, and the resulting material then immersed in, or mixed into, the stem cell collection composition of the invention. Any method of physical disruption can be used, provided that the method of disruption leaves a plurality, more preferably a majority, and more preferably at least 60%, 70%, 80%, 90%, 95%, 98%, or 99% of the cells in said organ viable, as determined by, e.g., trypan blue exclusion.

The placenta can be dissected into components prior to physical disruption and/or enzymatic digestion and stem cell recovery. For example, placental stem cells can be obtained from the amniotic membrane, chorion, placental cotyledons, or any combination thereof. Preferably, placental stem cells are obtained from placental tissue comprising amnion and chorion. Typically, placental stem cells can be obtained by disruption of a small block of placental tissue, e.g., a block of placental tissue that is about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900 or about 1000 cubic millimeters in volume.

A preferred stem cell collection composition comprises one or more tissue-disruptive enzyme(s). Enzymatic digestion preferably uses a combination of enzymes, e.g., a combination of a matrix metalloprotease and a neutral protease, for example, a combination of collagenase and dispase. In one embodiment, enzymatic digestion of placental tissue uses a combination of a matrix metalloprotease, a neutral protease, and a mucolytic enzyme for digestion of hyaluronic acid, such as a combination of collagenase, dispase, and hyaluronidase or a combination of LIBERASE (Boehringer Mannheim Corp., Indianapolis, Ind.) and hyaluronidase. Other enzymes that can be used to disrupt placenta tissue include papain, deoxyribonucleases, serine proteases, such as trypsin, chymotrypsin, or elastase. Serine proteases may be inhibited by alpha 2 microglobulin in serum and therefore the medium used for digestion is usually serum-free. EDTA and DNase are commonly used in enzyme digestion procedures to increase the efficiency of cell recovery. The digestate is preferably diluted so as to avoid trapping stem cells within the viscous digest.

Any combination of tissue digestion enzymes can be used. Typical concentrations for tissue digestion enzymes include, e.g., 50-200 U/mL for collagenase I and collagenase IV, 1-10 U/mL for dispase, and 10-100 U/mL for elastase. Proteases can be used in combination, that is, two or more proteases in the same digestion reaction, or can be used sequentially in order to liberate placental stem cells. For example, in one embodiment, a placenta, or part thereof, is digested first with an appropriate amount of collagenase I at 2 mg/ml for 30 minutes, followed by digestion with trypsin, 0.25%, for 10 minutes, at 37° C. Serine proteases are preferably used consecutively following use of other enzymes.

In another embodiment, the tissue can further be disrupted by the addition of a chelator, e.g., ethylene glycol bis(2-aminoethyl ether)-N,N,N′N′-tetraacetic acid (EGTA) or ethylenediaminetetraacetic acid (EDTA) to the stem cell collection composition comprising the stem cells, or to a solution in which the tissue is disrupted and/or digested prior to isolation of the stem cells with the stem cell collection composition.

It will be appreciated that where an entire placenta, or portion of a placenta comprising both fetal and maternal cells (for example, where the portion of the placenta comprises the chorion or cotyledons), the placental stem cells collected will comprise a mix of placental stem cells derived from both fetal and maternal sources. Where a portion of the placenta that comprises no, or a negligible number of, maternal cells (for example, amnion), the placental stem cells collected will comprise almost exclusively fetal placental stem cells.

5.3.4 Placental Perfusion

Placental stem cells can also be obtained by perfusion of the mammalian placenta. Methods of perfusing mammalian placenta to obtain stem cells are disclosed, e.g., in Hariri, U.S. Application Publication No. 2002/0123141, and in related U.S. Provisional Application No. 60/754,969, entitled “Improved Composition for Collecting and Preserving Placental Stem Cells and Methods of Using the Composition” filed on Dec. 29, 2005.

Placental stem cells can be collected by perfusion, e.g., through the placental vasculature, using, e.g., a stem cell collection composition as a perfusion solution. In one embodiment, a mammalian placenta is perfused by passage of perfusion solution through either or both of the umbilical artery and umbilical vein. The flow of perfusion solution through the placenta may be accomplished using, e.g., gravity flow into the placenta. Preferably, the perfusion solution is forced through the placenta using a pump, e.g., a peristaltic pump. The umbilical vein can be, e.g., cannulated with a cannula, e.g., a TEFLON® or plastic cannula, that is connected to a sterile connection apparatus, such as sterile tubing. The sterile connection apparatus is connected to a perfusion manifold.

In preparation for perfusion, the placenta is preferably oriented (e.g., suspended) in such a manner that the umbilical artery and umbilical vein are located at the highest point of the placenta. The placenta can be perfused by passage of a perfusion fluid, e.g., the stem cell collection composition of the invention, through the placental vasculature, or through the placental vasculature and surrounding tissue. In one embodiment, the umbilical artery and the umbilical vein are connected simultaneously to a pipette that is connected via a flexible connector to a reservoir of the perfusion solution. The perfusion solution is passed into the umbilical vein and artery. The perfusion solution exudes from and/or passes through the walls of the blood vessels into the surrounding tissues of the placenta, and is collected in a suitable open vessel from the surface of the placenta that was attached to the uterus of the mother during gestation. The perfusion solution may also be introduced through the umbilical cord opening and allowed to flow or percolate out of openings in the wall of the placenta which interfaced with the maternal uterine wall. In another embodiment, the perfusion solution is passed through the umbilical veins and collected from the umbilical artery, or is passed through the umbilical artery and collected from the umbilical veins.

In one embodiment, the proximal umbilical cord is clamped during perfusion, and more preferably, is clamped within 4-5 cm (centimeter) of the cord's insertion into the placental disc.

The first collection of perfusion fluid from a mammalian placenta during the exsanguination process is generally colored with residual red blood cells of the cord blood and/or placental blood. The perfusion fluid becomes more colorless as perfusion proceeds and the residual cord blood cells are washed out of the placenta. Generally from 30 to 100 ml (milliliter) of perfusion fluid is adequate to initially exsanguinate the placenta, but more or less perfusion fluid may be used depending on the observed results.

The volume of perfusion liquid used to collect placental stem cells may vary depending upon the number of stem cells to be collected, the size of the placenta, the number of collections to be made from a single placenta, etc. In various embodiments, the volume of perfusion liquid may be from 50 mL to 5000 mL, 50 mL to 4000 mL, 50 mL to 3000 mL, 100 mL to 2000 mL, 250 mL to 2000 mL, 500 mL to 2000 mL, or 750 mL to 2000 mL. Typically, the placenta is perfused with 700-800 mL of perfusion liquid following exsanguination.

The placenta can be perfused a plurality of times over the course of several hours or several days. Where the placenta is to be perfused a plurality of times, it may be maintained or cultured under aseptic conditions in a container or other suitable vessel, and perfused with the stem cell collection composition, or a standard perfusion solution (e.g., a normal saline solution such as phosphate buffered saline (“PBS”)) with or without an anticoagulant (e.g., heparin, warfarin sodium, coumarin, bishydroxycoumarin), and/or with or without an antimicrobial agent (e.g., β-mercaptoethanol (0.1 mM); antibiotics such as streptomycin (e.g., at 40-100 μg/ml), penicillin (e.g., at 40 U/ml), amphotericin B (e.g., at 0.5 μg/ml). In one embodiment, an isolated placenta is maintained or cultured for a period of time without collecting the perfusate, such that the placenta is maintained or cultured for 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, or 24 hours, or 2 or 3 or more days before perfusion and collection of perfusate. The perfused placenta can be maintained for one or more additional time(s), e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 or more hours, and perfused a second time with, e.g., 700-800 mL perfusion fluid. The placenta can be perfused 1, 2, 3, 4, 5 or more times, for example, once every 1, 2, 3, 4, 5 or 6 hours. In a preferred embodiment, perfusion of the placenta and collection of perfusion solution, e.g., stem cell collection composition, is repeated until the number of recovered nucleated cells falls below 100 cells/ml. The perfusates at different time points can be further processed individually to recover time-dependent populations of cells, e.g., stem cells. Perfusates from different time points can also be pooled.

Without wishing to be bound by any theory, after exsanguination and a sufficient time of perfusion of the placenta, placental stem cells are believed to migrate into the exsanguinated and perfused microcirculation of the placenta where, according to the methods of the invention, they are collected, preferably by washing into a collecting vessel by perfusion. Perfusing the isolated placenta not only serves to remove residual cord blood but also provide the placenta with the appropriate nutrients, including oxygen. The placenta may be cultivated and perfused with a similar solution which was used to remove the residual cord blood cells, preferably, without the addition of anticoagulant agents.

Perfusion according to the methods of the invention results in the collection of significantly more placental stem cells than the number obtainable from a mammalian placenta not perfused with said solution, and not otherwise treated to obtain stem cells (e.g., by tissue disruption, e.g., enzymatic digestion). In this context, “significantly more” means at least 10% more. Perfusion according to the methods of the invention yields significantly more placental stem cells than, e.g., the number of placental stem cells obtainable from culture medium in which a placenta, or portion thereof, has been cultured.

Stem cells can be isolated from placenta by perfusion with a solution comprising one or more proteases or other tissue-disruptive enzymes. In a specific embodiment, a placenta or portion thereof (e.g., amniotic membrane, amnion and chorion, placental lobule or cotyledon, or combination of any of the foregoing) is brought to 25-37° C., and is incubated with one or more tissue-disruptive enzymes in 200 mL of a culture medium for 30 minutes. Cells from the perfusate are collected, brought to 4° C., and washed with a cold inhibitor mix comprising 5 mM EDTA, 2 mM dithiothreitol and 2 mM beta-mercaptoethanol. The stem cells are washed after several minutes with a cold (e.g., 4° C.) stem cell collection composition of the invention.

It will be appreciated that perfusion using the pan method, that is, whereby perfusate is collected after it has exuded from the maternal side of the placenta, results in a mix of fetal and maternal cells. As a result, the cells collected by this method comprise a mixed population of placental stem cells of both fetal and maternal origin. In contrast, perfusion solely through the placental vasculature, whereby perfusion fluid is passed through one or two placental vessels and is collected solely through the remaining vessel(s), results in the collection of a population of placental stem cells almost exclusively of fetal origin.

5.3.5 Isolation, Sorting, and Characterization of Placental Stem Cells

Stem cells from mammalian placenta, whether obtained by perfusion or enyzmatic digestion, can initially be purified from (i.e., be isolated from) other cells by Ficoll gradient centrifugation. Such centrifugation can follow any standard protocol for centrifugation speed, etc. In one embodiment, for example, cells collected from the placenta are recovered from perfusate by centrifugation at 5000×g for 15 minutes at room temperature, which separates cells from, e.g., contaminating debris and platelets. In another embodiment, placental perfusate is concentrated to about 200 ml, gently layered over Ficoll, and centrifuged at about 1100×g for 20 minutes at 22° C., and the low-density interface layer of cells is collected for further processing.

Cell pellets can be resuspended in fresh stem cell collection composition, or a medium suitable for stem cell maintenance, e.g., IMDM serum-free medium containing 2 U/ml heparin and 2 mM EDTA (GibcoBRL, N.Y.). The total mononuclear cell fraction can be isolated, e.g., using Lymphoprep (Nycomed Pharma, Oslo, Norway) according to the manufacturer's recommended procedure.

As used herein, “isolating” placental stem cells means to remove at least 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95% or 99% of the cells with which the stem cells are normally associated in the intact mammalian placenta. A stem cell from an organ is “isolated” when it is present in a population of cells that comprises fewer than 50% of the cells with which the stem cell is normally associated in the intact organ.

Placental cells obtained by perfusion or digestion can, for example, be further, or initially, isolated by differential trypsinization using, e.g., a solution of 0.05% trypsin with 0.2% EDTA (Sigma, St. Louis Mo.). Differential trypsinization is possible because placental stem cells typically detach from plastic surfaces within about five minutes whereas other adherent populations typically require more than 20-30 minutes incubation. The detached placental stem cells can be harvested following trypsinization and trypsin neutralization, using, e.g., Trypsin Neutralizing Solution (TNS, Cambrex). In one embodiment of isolation of adherent cells, aliquots of, for example, about 5-10×10⁶ cells are placed in each of several T-75 flasks, preferably fibronectin-coated T75 flasks. In such an embodiment, the cells can be cultured with commercially available Mesenchymal Stem Cell Growth Medium (MSCGM) (Cambrex), and placed in a tissue culture incubator (37° C., 5% CO₂). After 10 to 15 days, non-adherent cells are removed from the flasks by washing with PBS. The PBS is then replaced by MSCGM. Flasks are preferably examined daily for the presence of various adherent cell types and in particular, for identification and expansion of clusters of fibroblastoid cells.

The number and type of cells collected from a mammalian placenta can be monitored, for example, by measuring changes in morphology and cell surface markers using standard cell detection techniques such as flow cytometry, cell sorting, immunocytochemistry (e.g., staining with tissue specific or cell-marker specific antibodies) fluorescence activated cell sorting (FACS), magnetic activated cell sorting (MACS), by examination of the morphology of cells using light or confocal microscopy, and/or by measuring changes in gene expression using techniques well known in the art, such as PCR and gene expression profiling. These techniques can be used, too, to identify cells that are positive for one or more particular markers. For example, using antibodies to CD34, one can determine, using the techniques above, whether a cell comprises a detectable amount of CD34; if so, the cell is CD34⁺. Likewise, if a cell produces enough OCT-4 RNA to be detectable by RT-PCR, or significantly more OCT-4 RNA than an adult cell, the cell is OCT-4+Antibodies to cell surface markers (e.g., CD markers such as CD34) and the sequence of stem cell-specific genes, such as OCT-4, are well-known in the art.

Placental cells, particularly cells that have been isolated by Ficoll separation, differential adherence, or a combination of both, may be sorted using a fluorescence activated cell sorter (FACS). Fluorescence activated cell sorting (FACS) is a well-known method for separating particles, including cells, based on the fluorescent properties of the particles (Kamarch, 1987, Methods Enzymol, 151:150-165). Laser excitation of fluorescent moieties in the individual particles results in a small electrical charge allowing electromagnetic separation of positive and negative particles from a mixture. In one embodiment, cell surface marker-specific antibodies or ligands are labeled with distinct fluorescent labels. Cells are processed through the cell sorter, allowing separation of cells based on their ability to bind to the antibodies used. FACS sorted particles may be directly deposited into individual wells of 96-well or 384-well plates to facilitate separation and cloning.

In one sorting scheme, stem cells from placenta are sorted on the basis of expression of the markers CD34, CD38, CD44, CD45, CD73, CD105, OCT-4 and/or HLA-G. This can be accomplished in connection with procedures to select stem cells on the basis of their adherence properties in culture. For example, an adherence selection stem can be accomplished before or after sorting on the basis of marker expression. In one embodiment, for example, cells are sorted first on the basis of their expression of CD34; CD34⁻ cells are retained, and cells that are CD200⁺HLA-G⁺, are separated from all other CD34⁻ cells. In another embodiment, cells from placenta are based on their expression of markers CD200 and/or HLA-G; for example, cells displaying either of these markers are isolated for further use. Cells that express, e.g., CD200 and/or HLA-G can, in a specific embodiment, be further sorted based on their expression of CD73 and/or CD105, or epitopes recognized by antibodies SH2, SH3 or SH4, or lack of expression of CD34, CD38 or CD45. For example, in one embodiment, placental cells are sorted by expression, or lack thereof, of CD200, HLA-G, CD73, CD105, CD34, CD38 and CD45, and placental cells that are CD200⁺, HLA-G⁺, CD73⁺, CD105⁺, CD34⁻, CD38⁻ and CD45⁻ are isolated from other placental cells for further use.

In another embodiment, magnetic beads can be used to separate cells. The cells may be sorted using a magnetic activated cell sorting (MACS) technique, a method for separating particles based on their ability to bind magnetic beads (0.5-100 μm diameter). A variety of useful modifications can be performed on the magnetic microspheres, including covalent addition of antibody that specifically recognizes a particular cell surface molecule or hapten. The beads are then mixed with the cells to allow binding. Cells are then passed through a magnetic field to separate out cells having the specific cell surface marker. In one embodiment, these cells can then isolated and re-mixed with magnetic beads coupled to an antibody against additional cell surface markers. The cells are again passed through a magnetic field, isolating cells that bound both the antibodies. Such cells can then be diluted into separate dishes, such as microtiter dishes for clonal isolation.

Placental stem cells can also be characterized and/or sorted based on cell morphology and growth characteristics. For example, placental stem cells can be characterized as having, and/or selected on the basis of, e.g., a fibroblastoid appearance in culture. Placental stem cells can also be characterized as having, and/or be selected, on the basis of their ability to form embryoid-like bodies. In one embodiment, for example, placental cells that are fibroblastoid in shape, express CD73 and CD105, and produce one or more embryoid-like bodies in culture are isolated from other placental cells. In another embodiment, OCT-4⁺ placental cells that produce one or more embryoid-like bodies in culture are isolated from other placental cells.

In another embodiment, placental stem cells can be identified and characterized by a colony forming unit assay. Colony forming unit assays are commonly known in the art, such as Mesen Cult™ medium (Stem Cell Technologies, Inc., Vancouver British Columbia)

Placental stem cells can be assessed for viability, proliferation potential, and longevity using standard techniques known in the art, such as trypan blue exclusion assay, fluorescein diacetate uptake assay, propidium iodide uptake assay (to assess viability); and thymidine uptake assay, MTT cell proliferation assay (to assess proliferation). Longevity may be determined by methods well known in the art, such as by determining the maximum number of population doubling in an extended culture.

Placental stem cells can also be separated from other placental cells using other techniques known in the art, e.g., selective growth of desired cells (positive selection), selective destruction of unwanted cells (negative selection); separation based upon differential cell agglutinability in the mixed population as, for example, with soybean agglutinin; freeze-thaw procedures; filtration; conventional and zonal centrifugation; centrifugal elutriation (counter-streaming centrifugation); unit gravity separation; countercurrent distribution; electrophoresis; and the like.

5.4 Culture of Placental Stem Cells

5.4.1 Culture Media

Isolated placental stem cells, or placental stem cell population, or cells or placental tissue from which placental stem cells grow out, can be used to initiate, or seed, cell cultures. Cells are generally transferred to sterile tissue culture vessels either uncoated or coated with extracellular matrix or ligands such as laminin, collagen (e.g., native or denatured), gelatin, fibronectin, ornithine, vitronectin, and extracellular membrane protein (e.g., MATRIGEL (BD Discovery Labware, Bedford, Mass.)).

Placental stem cells can be cultured in any medium, and under any conditions, recognized in the art as acceptable for the culture of stem cells. Preferably, the culture medium comprises serum. Placental stem cells can be cultured in, for example, DMEM-LG (Dulbecco's Modified Essential Medium, low glucose)/MCDB 201 (chick fibroblast basal medium) containing ITS (insulin-transferrin-selenium), LA+BSA (linoleic acid-bovine serum albumin), dextrose, L-ascorbic acid, PDGF, EGF, IGF-1, and penicillin/streptomycin; DMEM-HG (high glucose) comprising 10% fetal bovine serum (FBS); DMEM-HG comprising 15% FBS; IMDM (Iscove's modified Dulbecco's medium) comprising 10% FBS, 10% horse serum, and hydrocortisone; M199 comprising 10% FBS, EGF, and heparin; aMEM (minimal essential medium) comprising 10% FBS, GlutaMAX™ and gentamicin; DMEM comprising 10% FBS, GlutaMAX™ and gentamicin, etc. A preferred medium is DMEM-LG/MCDB-201 comprising 2% FBS, ITS, LA+BSA, dextrose, L-ascorbic acid, PDGF, EGF, and penicillin/streptomycin.

Other media in that can be used to culture placental stem cells include DMEM (high or low glucose), Eagle's basal medium, Ham's F10 medium (F10), Ham's F-12 medium (F12), Iscove's modified Dulbecco's medium, Mesenchymal Stem Cell Growth Medium (MSCGM), Liebovitz's L-15 medium, MCDB, DMIEM/F12, RPMI 1640, advanced DMEM (Gibco), DMEM/MCDB201 (Sigma), and CELL-GRO FREE.

The culture medium can be supplemented with one or more components including, for example, serum (e.g., fetal bovine serum (FBS), preferably about 2-15% (v/v); equine (horse) serum (ES); human serum (HS)); beta-mercaptoethanol (BME), preferably about 0.001% (v/v); one or more growth factors, for example, platelet-derived growth factor (PDGF), epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), insulin-like growth factor-1 (IGF-1), leukemia inhibitory factor (LIF), vascular endothelial growth factor (VEGF), and erythropoietin (EPO); amino acids, including L-valine; and one or more antibiotic and/or antimycotic agents to control microbial contamination, such as, for example, penicillin G, streptomycin sulfate, amphotericin B, gentamicin, and nystatin, either alone or in combination.

5.4.2 Expansion and Proliferation of Placental Stem Cells

Once an isolated placental stem cell, or isolated population of stem cells (e.g., a stem cell or population of stem cells separated from at least 50% of the placental cells with which the stem cell or population of stem cells is normally associated in vivo), the stem cell or population of stem cells can be proliferated and expanded in vitro. For example, a population of placental stem cells can be cultured in tissue culture containers, e.g., dishes, flasks, multiwell plates, or the like, for a sufficient time for the stem cells to proliferate to 70-90% confluence, that is, until the stem cells and their progeny occupy 70-90% of the culturing surface area of the tissue culture container.

Placental stem cells can be seeded in culture vessels at a density that allows cell growth. For example, the cells may be seeded at low density (e.g., about 1,000 to about 5,000 cells/cm ²) to high density (e.g., about 50,000 or more cells/cm²). In a preferred embodiment, the cells are cultured at about 0 to about 5 percent by volume CO₂ in air. In some preferred embodiments, the cells are cultured at about 2 to about 25 percent O₂ in air, preferably about 5 to about 20 percent O₂ in air. The cells preferably are cultured at about 25° C. to about 40° C., preferably 37° C. The cells are preferably cultured in an incubator. The culture medium can be static or agitated, for example, using a bioreactor. Placental stem cells preferably are grown under low oxidative stress (e.g., with addition of glutathione, ascorbic acid, catalase, tocopherol, N-acetylcysteine, or the like).

Once 70%-90% confluence is obtained, the cells may be passaged. For example, the cells can be enzymatically treated, e.g., trypsinized, using techniques well-known in the art, to separate them from the tissue culture surface. After removing the cells by pipetting and counting the cells, about 20,000-100,000 stem cells, preferably about 50,000 stem cells, are passaged to a new culture container containing fresh culture medium. Typically, the new medium is the same type of medium from which the stem cells were removed. The invention encompasses populations of placental stem cells that have been passaged at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, or 20 times, or more.

5.4.3 Placental Stem Cell Populations

The invention provides populations of placental stem cells. Placental stem cell population can be isolated directly from one or more placentas; that is, the placental stem cell population can be a population of placental cells, comprising placental stem cells, obtained from, or contained within, perfusate, or obtained from, or contained within, digestate (that is, the collection of cells obtained by enzymatic digestion of a placenta or part thereof). Isolated placental stem cells of the invention can also be cultured and expanded to produce placental stem cell populations. Populations of placental cells comprising placental stem cells can also be cultured and expanded to produce placental stem cell populations.

Placental stem cell populations of the invention comprise placental stem cells, for example, placental stem cells as described herein. In various embodiments, at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or 99% of the cells in an isolated placental stem cell population are placental stem cells. That is, a placental stem cell population can comprise, e.g., as much as 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% non-stem cells.

The invention provides methods of producing isolated placental stem cell population by, e.g., selecting placental stem cells, whether derived from enzymatic digestion or perfusion, that express particular markers and/or particular culture or morphological characteristics. In one embodiment, for example, the invention provides a method of producing a cell population comprising selecting placental cells that (a) adhere to a substrate, and (b) express CD200 and HLA-G; and isolating said cells from other cells to form a cell population. In another embodiment, the method of producing a cell population comprises selecting placental cells that (a) adhere to a substrate, and (b) express CD73, CD105, and CD200; and isolating said cells from other cells to form a cell population. In another embodiment, the method of producing a cell population comprises selecting placental cells that (a) adhere to a substrate and (b) express CD200 and OCT-4; and isolating said cells from other cells to form a cell population. In another embodiment, the method of producing a cell population comprises selecting placental cells that (a) adhere to a substrate, (b) express CD73 and CD105, and (c) facilitate the formation of one or more embryoid-like bodies in a population of placental cells comprising said stem cell when said population is cultured under conditions that allow for the formation of an embryoid-like body; and isolating said cells from other cells to form a cell population. In another embodiment, the method of producing a cell population comprises selecting placental cells that (a) adhere to a substrate, and (b) express CD73, CD105 and HLA-G; and isolating said cells from other cells to form a cell population. In another embodiment, the method of producing a cell population comprises selecting placental cells that (a) adhere to a substrate, (b) express OCT-4, and (c) facilitate the formation of one or more embryoid-like bodies in a population of placental cells comprising said stem cell when said population is cultured under conditions that allow for the formation of an embryoid-like body; and isolating said cells from other cells to form a cell population. In any of the above embodiments, the method can additionally comprise selecting placental cells that express ABC-p (a placenta-specific ABC transporter protein; see, e.g., Allikmets et al., Cancer Res. 58(23):5337-9 (1998)). The method can also comprise selecting cells exhibiting at least one characteristic specific to, e.g., a mesenchymal stem cell, for example, expression of CD29, expression of CD44, expression of CD90, or expression of a combination of the foregoing.

In the above embodiments, the substrate can be any surface on which culture and/or selection of cells, e.g., placental stem cells, can be accomplished. Typically, the substrate is plastic, e.g., tissue culture dish or multiwell plate plastic. Tissue culture plastic can be coated with a biomolecule, e.g., laminin or fibronectin.

Cells, e.g., placental stem cells, can be selected for a placental stem cell population by any means known in the art of cell selection. For example, cells can be selected using an antibody or antibodies to one or more cell surface markers, for example, in flow cytometry or FACS. Selection can be accomplished using antibodies in conjunction with magnetic beads. Antibodies that are specific for certain stem cell-related markers are known in the art. For example, antibodies to OCT-4 (Abcam, Cambridge, Mass.), CD200 (Abcam), HLA-G (Abcam), CD73 (BD Biosciences Pharmingen, San Diego, Calif.), CD105 (Abcam; BioDesign International, Saco, Me.), etc. Antibodies to other markers are also available commercially, e.g., CD34, CD38 and CD45 are available from, e.g., StemCell Technologies or BioDesign International.

The isolated placental stem cell population can comprise placental cells that are not stem cells, or cells that are not placental cells.

Isolated placental stem cell populations can be combined with one or more populations of non-stem cells or non-placental cells. For example, an isolated population of placental stem cells can be combined with blood (e.g., placental blood or umbilical cord blood), blood-derived stem cells (e.g., stem cells derived from placental blood or umbilical cord blood), populations of blood-derived nucleated cells, bone marrow-derived mesenchymal cells, bone-derived stem cell populations, crude bone marrow, adult (somatic) stem cells, populations of stem cells contained within tissue, cultured stem cells, populations of fully-differentiated cells (e.g., chondrocytes, fibroblasts, amniotic cells, osteoblasts, muscle cells, cardiac cells, etc.) and the like. Cells in an isolated placental stem cell population can be combined with a plurality of cells of another type in ratios of about 100,000,000:1, 50,000,000:1, 20,000,000:1, 10,000,000:1, 5,000,000:1, 2,000,000:1, 1,000,000:1, 500,000:1, 200,000:1, 100,000:1, 50,000:1, 20,000:1, 10,000:1, 5,000:1, 2,000:1, 1,000:1, 500:1,200:1, 100:1, 50:1, 20:1, 10:1, 5:1, 2:1, 1:1; 1:2; 1:5; 1:10; 1:100; 1:200; 1:500; 1:1,000; 1:2,000; 1:5,000; 1:10,000; 1:20,000; 1:50,000; 1:100,000; 1:500,000; 1:1,000,000; 1:2,000,000; 1:5,000,000; 1:10,000,000; 1:20,000,000; 1:50,000,000; or about 1:100,000,000, comparing numbers of total nucleated cells in each population. Cells in an isolated placental stem cell population can be combined with a plurality of cells of a plurality of cell types, as well.

In one, an isolated population of placental stem cells is combined with a plurality of hematopoietic stem cells. Such hematopoietic stem cells can be, for example, contained within unprocessed placental, umbilical cord blood or peripheral blood; in total nucleated cells from placental blood, umbilical cord blood or peripheral blood; in an isolated population of CD34⁺ cells from placental blood, umbilical cord blood or peripheral blood; in unprocessed bone marrow; in total nucleated cells from bone marrow; in an isolated population of CD34⁺ cells from bone marrow, or the like.

5.5 Preservation of Placental Stem Cells

Placental stem cells can be preserved, that is, placed under conditions that allow for long-term storage, or conditions that inhibit cell death by, e.g., apoptosis or necrosis.

Placental stem cells can be preserved using, e.g., a composition comprising an apoptosis inhibitor, necrosis inhibitor and/or an oxygen-carrying perfluorocarbon, as described in related U.S. Provisional Application No. 60/754,969, entitled “Improved Composition for Collecting and Preserving Placental Stem Cells and Methods of Using the Composition” filed on Dec. 25, 2005. In one embodiment, the invention provides a method of preserving a population of stem cells comprising contacting said population of stem cells with a stem cell collection composition comprising an inhibitor of apoptosis and an oxygen-carrying perfluorocarbon, wherein said inhibitor of apoptosis is present in an amount and for a time sufficient to reduce or prevent apoptosis in the population of stem cells, as compared to a population of stem cells not contacted with the inhibitor of apoptosis. In a specific embodiment, said inhibitor of apoptosis is a caspase inhibitor. In another specific embodiment, said inhibitor of apoptosis is a JNK inhibitor. In a more specific embodiment, said JNK inhibitor does not modulate differentiation or proliferation of said stem cells. In another embodiment, said stem cell collection composition comprises said inhibitor of apoptosis and said oxygen-carrying perfluorocarbon in separate phases. In another embodiment, said stem cell collection composition comprises said inhibitor of apoptosis and said oxygen-carrying perfluorocarbon in an emulsion. In another embodiment, the stem cell collection composition additionally comprises an emulsifier, e.g., lecithin. In another embodiment, said apoptosis inhibitor and said perfluorocarbon are between about 0° C. and about 25° C. at the time of contacting the stem cells. In another more specific embodiment, said apoptosis inhibitor and said perfluorocarbon are between about 2° C. and 10° C., or between about 2° C. and about 5° C., at the time of contacting the stem cells. In another more specific embodiment, said contacting is performed during transport of said population of stem cells. In another more specific embodiment, said contacting is performed during freezing and thawing of said population of stem cells.

In another embodiment, the invention provides a method of preserving a population of placental stem cells comprising contacting said population of stem cells with an inhibitor of apoptosis and an organ-preserving compound, wherein said inhibitor of apoptosis is present in an amount and for a time sufficient to reduce or prevent apoptosis in the population of stem cells, as compared to a population of stem cells not contacted with the inhibitor of apoptosis. In a specific embodiment, the organ-preserving compound is UW solution (described in U.S. Pat. No. 4,798,824; also known as ViaSpan; see also Southard et al., Transplantation 49(2):251-257 (1990)) or a solution described in Stern et al., U.S. Pat. No. 5,552,267. In another embodiment, said organ-preserving compound is hydroxyethyl starch, lactobionic acid, raffinose, or a combination thereof. In another embodiment, the stem cell collection composition additionally comprises an oxygen-carrying perfluorocarbon, either in two phases or as an emulsion.

In another embodiment of the method, placental stem cells are contacted with a stem cell collection composition comprising an apoptosis inhibitor and oxygen-carrying perfluorocarbon, organ-preserving compound, or combination thereof, during perfusion. In another embodiment, said stem cells are contacted during a process of tissue disruption, e.g., enzymatic digestion. In another embodiment, placental stem cells are contacted with said stem cell collection compound after collection by perfusion, or after collection by tissue disruption, e.g., enzymatic digestion.

Typically, during placental cell collection, enrichment and isolation, it is preferable to minimize or eliminate cell stress due to hypoxia and mechanical stress. In another embodiment of the method, therefore, a stem cell, or population of stem cells, is exposed to a hypoxic condition during collection, enrichment or isolation for less than six hours during said preservation, wherein a hypoxic condition is a concentration of oxygen that is less than normal blood oxygen concentration. In a more specific embodiment, said population of stem cells is exposed to said hypoxic condition for less than two hours during said preservation. In another more specific embodiment, said population of stem cells is exposed to said hypoxic condition for less than one hour, or less than thirty minutes, or is not exposed to a hypoxic condition, during collection, enrichment or isolation. In another specific embodiment, said population of stem cells is not exposed to shear stress during collection, enrichment or isolation.

The placental stem cells of the invention can be cryopreserved, e.g., in cryopreservation medium in small containers, e.g., ampoules. Suitable cryopreservation medium includes, but is not limited to, culture medium including, e.g., growth medium, or cell freezing medium, for example commercially available cell freezing medium, e.g., C2695, C2639 or C6039 (Sigma). Cryopreservation medium preferably comprises DMSO (dimethylsulfoxide), at a concentration of, e.g., about 10% (v/v). Cryopreservation medium may comprise additional agents, for example, methylcellulose and/or glycerol. Placental stem cells are preferably cooled at about 1° C./min during cryopreservation. A preferred cryopreservation temperature is about −80° C. to about −180° C., preferably about −125° C. to about −140° C. Cryopreserved cells can be transferred to liquid nitrogen prior to thawing for use. In some embodiments, for example, once the ampoules have reached about −90° C., they are transferred to a liquid nitrogen storage area. Cryopreserved cells preferably are thawed at a temperature of about 25° C. to about 40° C., preferably to a temperature of about 37° C.

5.6 Uses of Placental Stem Cells

5.6.1 Compositions Comprising Placental Stem Cells

The methods of immunosuppression of the present invention can use compositions comprising placental stem cells, or biomolecules therefrom. In the same manner, the pluralities and populations of placental stem cells of the present invention can be combined with any physiologically-acceptable or medically-acceptable compound, composition or device for use in, e.g., research or therapeutics.

5.6.1.1 Cryopreserved Placental Stem Cells

The immunosuppressive placental stem cell populations of the invention can be preserved, for example, cryopreserved for later use. Methods for cryopreservation of cells, such as stem cells, are well known in the art. Placental stem cell populations can be prepared in a form that is easily administrable to an individual. For example, the invention provides a placental stem cell population that is contained within a container that is suitable for medical use. Such a container can be, for example, a sterile plastic bag, flask, jar, or other container from which the placental stem cell population can be easily dispensed. For example, the container can be a blood bag or other plastic, medically-acceptable bag suitable for the intravenous administration of a liquid to a recipient. The container is preferably one that allows for cryopreservation of the combined stem cell population.

Cryopreserved immunosuppressive placental stem cell populations can comprise placental stem cells derived from a single donor, or from multiple donors. The placental stem cell population can be completely HLA-matched to an intended recipient, or partially or completely HLA-mismatched.

Thus, in one embodiment, the invention provides a composition comprising an immunosuppressive placental stem cell population in a container. In a specific embodiment, the stem cell population is cryopreserved. In another specific embodiment, the container is a bag, flask, or jar. In more specific embodiment, said bag is a sterile plastic bag. In a more specific embodiment, said bag is suitable for, allows or facilitates intravenous administration of said placental stem cell population. The bag can comprise multiple lumens or compartments that are interconnected to allow mixing of the placental stem cells and one or more other solutions, e.g., a drug, prior to, or during, administration. In another specific embodiment, the composition comprises one or more compounds that facilitate cryopreservation of the combined stem cell population. In another specific embodiment, said placental stem cell population is contained within a physiologically-acceptable aqueous solution. In a more specific embodiment, said physiologically-acceptable aqueous solution is a 0.9% NaCl solution. In another specific embodiment, said placental stem cell population comprises placental cells that are HLA-matched to a recipient of said stem cell population. In another specific embodiment, said combined stem cell population comprises placental cells that are at least partially HLA-mismatched to a recipient of said stem cell population. In another specific embodiment, said placental stem cells are derived from a plurality of donors.

5.6.1.2 Pharmaceutical Compositions

Immunosuppressive populations of placental stem cells, or populations of cells comprising placental stem cells, can be formulated into pharmaceutical compositions for use in vivo. Such pharmaceutical compositions comprise a population of placental stem cells, or a population of cells comprising placental stem cells, in a pharmaceutically-acceptable carrier, e.g., a saline solution or other accepted physiologically-acceptable solution for in vivo administration. Pharmaceutical compositions of the invention can comprise any of the placental stem cell populations, or placental stem cell types, described elsewhere herein. The pharmaceutical compositions can comprise fetal, maternal, or both fetal and maternal placental stem cells. The pharmaceutical compositions of the invention can further comprise placental stem cells obtained from a single individual or placenta, or from a plurality of individuals or placentae.

The pharmaceutical compositions of the invention can comprise any immunosuppressive number of placental stem cells. For example, a single unit dose of placental stem cells can comprise, in various embodiments, about, at least, or no more than 1×10⁵, 5×10⁵, 1×10⁶, 5×10⁶, 1×10⁷, 5×10⁷, 1×10⁸, 5×10⁸, 1×10⁹, 5×10⁹, 1×10¹⁰, 5×10¹⁰, 1×10¹¹ or more placental stem cells.

The pharmaceutical compositions of the invention comprise populations of cells that comprise 50% viable cells or more (that is, at least 50% of the cells in the population are functional or living). Preferably, at least 60% of the cells in the population are viable. More preferably, at least 70%, 80%, 90%, 95%, or 99% of the cells in the population in the pharmaceutical composition are viable.

The pharmaceutical compositions of the invention can comprise one or more compounds that, e.g., facilitate engraftment (e.g., anti-T-cell receptor antibodies, an immunosuppressant, or the like); stabilizers such as albumin, dextran 40, gelatin, hydroxyethyl starch, and the like.

5.6.1.3 Placental Stem Cell Conditioned Media

The placental stem cells of the invention can be used to produce conditioned medium that is immunosuppressive, that is, medium comprising one or more biomolecules secreted or excreted by the stem cells that have a detectable immunosuppressive effect on a plurality of one or more types of immune cells. In various embodiments, the conditioned medium comprises medium in which placental stem cells have grown for at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or more days. In other embodiments, the conditioned medium comprises medium in which placental stem cells have grown to at least 30%, 40%, 50%, 60%, 70%, 80%, 90% confluence, or up to 100% confluence. Such conditioned medium can be used to support the culture of a separate population of placental stem cells, or stem cells of another kind. In another embodiment, the conditioned medium comprises medium in which placental stem cells have been differentiated into an adult cell type. In another embodiment, the conditioned medium of the invention comprises medium in which placental stem cells and non-placental stem cells have been cultured.

Thus, in one embodiment, the invention provides a composition comprising culture medium from a culture of placental stem cells, wherein said placental stem cells (a) adhere to a substrate; (b) express CD200 and HLA-G, or express CD73, CD105, and CD200, or express CD200 and OCT-4, or express CD73, CD105, and HLA-G, or express CD73 and CD105 and facilitate the formation of one or more embryoid-like bodies in a population of placental cells that comprise the placental stem cells, when said population is cultured under conditions that allow formation of embryoid-like bodies, or express OCT-4 and facilitate the formation of one or more embryoid-like bodies in a population of placental cells that comprise the placental stem cells when said population is cultured under conditions that allow formation of embryoid-like bodies; and (c) detectably suppress CD4⁺ or CD8⁺ T cell proliferation in an MLR (mixed lymphocyte reaction), wherein said culture of placental stem cells has been cultured in said medium for 24 hours or more. In a specific embodiment, the composition further comprises a plurality of said placental stem cells. In another specific embodiment, the composition comprises a plurality of non-placental cells. In a more specific embodiment, said non-placental cells comprise CD34⁺ cells, e.g., hematopoietic progenitor cells, such as peripheral blood hematopoietic progenitor cells, cord blood hematopoietic progenitor cells, or placental blood hematopoietic progenitor cells. The non-placental cells can also comprise other stem cells, such as mesenchymal stem cells, e.g., bone marrow-derived mesenchymal stem cells. The non-placental cells can also be one or more types of adult cells or cell lines. In another specific embodiment, the composition comprises an antiproliferative agent, e.g., an anti-MIP-1α or anti-MIP-1β antibody.

5.6.1.4 Matrices Comprising Placental Stem Cells

The invention further comprises matrices, hydrogels, scaffolds, and the like that comprise an immunosuppresive population of placental stem cells.

Placental stem cells of the invention can be seeded onto a natural matrix, e.g., a placental biomaterial such as an amniotic membrane material. Such an amniotic membrane material can be, e.g., amniotic membrane dissected directly from a mammalian placenta; fixed or heat-treated amniotic membrane, substantially dry (i.e., <20% H₂O) amniotic membrane, chorionic membrane, substantially dry chorionic membrane, substantially dry amniotic and chorionic membrane, and the like. Preferred placental biomaterials on which placental stem cells can be seeded are described in Hariri, U.S. Application Publication No. 2004/0048796.

Placental stem cells of the invention can be suspended in a hydrogel solution suitable for, e.g., injection. Suitable hydrogels for such compositions include self-assembling peptides, such as RAD16. In one embodiment, a hydrogel solution comprising the cells can be allowed to harden, for instance in a mold, to form a matrix having cells dispersed therein for implantation. Placental stem cells in such a matrix can also be cultured so that the cells are mitotically expanded prior to implantation. The hydrogel is, e.g., an organic polymer (natural or synthetic) that is cross-linked via covalent, ionic, or hydrogen bonds to create a three-dimensional open-lattice structure that entraps water molecules to form a gel. Hydrogel-forming materials include polysaccharides such as alginate and salts thereof, peptides, polyphosphazines, and polyacrylates, which are crosslinked ionically, or block polymers such as polyethylene oxide-polypropylene glycol block copolymers which are crosslinked by temperature or pH, respectively. In some embodiments, the hydrogel or matrix of the invention is biodegradable.

In some embodiments of the invention, the formulation comprises an in situ polymerizable gel (see., e.g., U.S. Patent Application Publication 2002/0022676; Anseth et al., J. Control Release, 78(1-3):199-209 (2002); Wang et al., Biomaterials, 24(22):3969-80 (2003).

In some embodiments, the polymers are at least partially soluble in aqueous solutions, such as water, buffered salt solutions, or aqueous alcohol solutions, that have charged side groups, or a monovalent ionic salt thereof. Examples of polymers having acidic side groups that can be reacted with cations are poly(phosphazenes), poly(acrylic acids), poly(methacrylic acids), copolymers of acrylic acid and methacrylic acid, poly(vinyl acetate), and sulfonated polymers, such as sulfonated polystyrene. Copolymers having acidic side groups formed by reaction of acrylic or methacrylic acid and vinyl ether monomers or polymers can also be used. Examples of acidic groups are carboxylic acid groups, sulfonic acid groups, halogenated (preferably fluorinated) alcohol groups, phenolic OH groups, and acidic OH groups.

The placental stem cells of the invention or co-cultures thereof can be seeded onto a three-dimensional framework or scaffold and implanted in vivo. Such a framework can be implanted in combination with any one or more growth factors, cells, drugs or other components that stimulate tissue formation or otherwise enhance or improve the practice of the invention.

Examples of scaffolds that can be used in the present invention include nonwoven mats, porous foams, or self assembling peptides. Nonwoven mats can be formed using fibers comprised of a synthetic absorbable copolymer of glycolic and lactic acids (e.g., PGA/PLA) (VICRYL, Ethicon, Inc., Somerville, N.J.). Foams, composed of, e.g., poly(ε-caprolactone)/poly(glycolic acid) (PCL/PGA) copolymer, formed by processes such as freeze-drying, or lyophilization (see, e.g., U.S. Pat. No. 6,355,699), can also be used as scaffolds.

Placental stem cells of the invention can also be seeded onto, or contacted with, a physiologically-acceptable ceramic material including, but not limited to, mono-, di-, tri-, alpha-tri-, beta-tri-, and tetra-calcium phosphate, hydroxyapatite, fluoroapatites, calcium sulfates, calcium fluorides, calcium oxides, calcium carbonates, magnesium calcium phosphates, biologically active glasses such as BIOGLASS®, and mixtures thereof. Porous biocompatible ceramic materials currently commercially available include SURGIBONE® (CanMedica Corp., Canada), ENDOBON® (Merck Biomaterial France, France), CEROS® (Mathys, A G, Bettlach, Switzerland), and mineralized collagen bone grafting products such as HEALOS™ (DePuy, Inc., Raynham, Mass.) and VITOSS®, RHAKOSS™, and CORTOSS® (Orthovita, Malvern, Pa.). The framework can be a mixture, blend or composite of natural and/or synthetic materials.

In another embodiment, placental stem cells can be seeded onto, or contacted with, a felt, which can be, e.g., composed of a multifilament yarn made from a bioabsorbable material such as PGA, PLA, PCL copolymers or blends, or hyaluronic acid.

The placental stem cells of the invention can, in another embodiment, be seeded onto foam scaffolds that may be composite structures. Such foam scaffolds can be molded into a useful shape, such as that of a portion of a specific structure in the body to be repaired, replaced or augmented. In some embodiments, the framework is treated, e.g., with 0.1M acetic acid followed by incubation in polylysine, PBS, and/or collagen, prior to inoculation of the cells of the invention in order to enhance cell attachment. External surfaces of a matrix may be modified to improve the attachment or growth of cells and differentiation of tissue, such as by plasma-coating the matrix, or addition of one or more proteins (e.g., collagens, elastic fibers, reticular fibers), glycoproteins, glycosaminoglycans (e.g., heparin sulfate, chondroitin-4-sulfate, chondroitin-6-sulfate, dermatan sulfate, keratin sulfate, etc.), a cellular matrix, and/or other materials such as, but not limited to, gelatin, alginates, agar, agarose, and plant gums, and the like.

In some embodiments, the scaffold comprises, or is treated with, materials that render it non-thrombogenic. These treatments and materials may also promote and sustain endothelial growth, migration, and extracellular matrix deposition. Examples of these materials and treatments include but are not limited to natural materials such as basement membrane proteins such as laminin and Type IV collagen, synthetic materials such as EPTFE, and segmented polyurethaneurea silicones, such as PURSPAN™ (The Polymer Technology Group, Inc., Berkeley, Calif.). The scaffold can also comprise anti-thrombotic agents such as heparin; the scaffolds can also be treated to alter the surface charge (e.g., coating with plasma) prior to seeding with placental stem cells.

5.6.2 Immortalized Placental Stem Cell Lines

Mammalian placental cells can be conditionally immortalized by transfection with any suitable vector containing a growth-promoting gene, that is, a gene encoding a protein that, under appropriate conditions, promotes growth of the transfected cell, such that the production and/or activity of the growth-promoting protein is regulatable by an external factor. In a preferred embodiment the growth-promoting gene is an oncogene such as, but not limited to, v-myc, N-myc, c-myc, p53, SV40 large T antigen, polyoma large T antigen, E1 a adenovirus or E7 protein of human papillomavirus.

External regulation of the growth-promoting protein can be achieved by placing the growth-promoting gene under the control of an externally-regulatable promoter, e.g., a promoter the activity of which can be controlled by, for example, modifying the temperature of the transfected cells or the composition of the medium in contact with the cells. in one embodiment, a tetracycline (tet)-controlled gene expression system can be employed (see Gossen et al., Proc. Natl. Acad. Sci. USA 89:5547-5551, 1992; Hoshimaru et al., Proc. Natl. Acad. Sci. USA 93:1518-1523, 1996). In the absence of tet, a tet-controlled transactivator (tTA) within this vector strongly activates transcription from ph_(CMV*−1), a minimal promoter from human cytomegalovirus fused to tet operator sequences. tTA is a fusion protein of the repressor (tetR) of the transposon-10-derived tet resistance operon of Escherichia coli and the acidic domain of VP16 of herpes simplex virus. Low, non-toxic concentrations of tet (e.g., 0.01-1.0 μg/mL) almost completely abolish transactivation by tTA.

In one embodiment, the vector further contains a gene encoding a selectable marker, e.g., a protein that confers drug resistance. The bacterial neomycin resistance gene (neo^(R)) is one such marker that may be employed within the present invention. Cells carrying neo^(R) may be selected by means known to those of ordinary skill in the art, such as the addition of, e.g., 100-200 μg/mL G418 to the growth medium.

Transfection can be achieved by any of a variety of means known to those of ordinary skill in the art including, but not limited to, retroviral infection. In general, a cell culture may be transfected by incubation with a mixture of conditioned medium collected from the producer cell line for the vector and DMEM/F12 containing N2 supplements. For example, a placental cell culture prepared as described above may be infected after, e.g., five days in vitro by incubation for about 20 hours in one volume of conditioned medium and two volumes of DMEM/F12 containing N2 supplements. Transfected cells carrying a selectable marker may then be selected as described above.

Following transfection, cultures are passaged onto a surface that permits proliferation, e.g., allows at least 30% of the cells to double in a 24 hour period. Preferably, the substrate is a polyornithine/laminin substrate, consisting of tissue culture plastic coated with polyornithine (10 μg/mL) and/or laminin (10 μg/mL), a polylysine/laminin substrate or a surface treated with fibronectin. Cultures are then fed every 3-4 days with growth medium, which may or may not be supplemented with one or more proliferation-enhancing factors. Proliferation-enhancing factors may be added to the growth medium when cultures are less than 50% confluent.

The conditionally-immortalized placental stem cell lines can be passaged using standard techniques, such as by trypsinization, when 80-95% confluent. Up to approximately the twentieth passage, it is, in some embodiments, beneficial to maintain selection (by, for example, the addition of G418 for cells containing a neomycin resistance gene). Cells may also be frozen in liquid nitrogen for long-term storage.

Clonal cell lines can be isolated from a conditionally-immortalized human placental stem cell line prepared as described above. In general, such clonal cell lines may be isolated using standard techniques, such as by limit dilution or using cloning rings, and expanded. Clonal cell lines may generally be fed and passaged as described above.

Conditionally-immortalized human placental stem cell lines, which may, but need not, be clonal, may generally be induced to differentiate by suppressing the production and/or activity of the growth-promoting protein under culture conditions that facilitate differentiation. For example, if the gene encoding the growth-promoting protein is under the control of an externally-regulatable promoter, the conditions, e.g., temperature or composition of medium, may be modified to suppress transcription of the growth-promoting gene. For the tetracycline-controlled gene expression system discussed above, differentiation can be achieved by the addition of tetracycline to suppress transcription of the growth-promoting gene. In general, 1 μg/mL tetracycline for 4-5 days is sufficient to initiate differentiation. To promote further differentiation, additional agents may be included in the growth medium.

5.6.3 Assays

The placental stem cells for the present invention can be used in assays to determine the influence of culture conditions, environmental factors, molecules (e.g., biomolecules, small inorganic molecules. etc.) and the like on stem cell proliferation, expansion, and/or differentiation, compared to placental stem cells not exposed to such conditions.

In a preferred embodiment, the placental stem cells of the present invention are assayed for changes in proliferation, expansion or differentiation upon contact with a molecule. In one embodiment, for example, the invention provides a method of identifying a compound that modulates the proliferation of a plurality of placental stem cells, comprising contacting said plurality of stem cells with said compound under conditions that allow proliferation, wherein if said compound causes a detectable change in proliferation of said plurality of stem cells compared to a plurality of stem cells not contacted with said compound, said compound is identified as a compound that modulates proliferation of placental stem cells. In a specific embodiment, said compound is identified as an inhibitor of proliferation. In another specific embodiment, said compound is identified as an enhancer of proliferation.

In another embodiment, the invention provides a method of identifying a compound that modulates the expansion of a plurality of placental stem cells, comprising contacting said plurality of stem cells with said compound under conditions that allow expansion, wherein if said compound causes a detectable change in expansion of said plurality of stem cells compared to a plurality of stem cells not contacted with said compound, said compound is identified as a compound that modulates expansion of placental stem cells. In a specific embodiment, said compound is identified as an inhibitor of expansion. In another specific embodiment, said compound is identified as an enhancer of expansion.

In another embodiment, the invention provides a method of identifying a compound that modulates the differentiation of a placental stem cell, comprising contacting said stem cells with said compound under conditions that allow differentiation, wherein if said compound causes a detectable change in differentiation of said stem cells compared to a stem cell not contacted with said compound, said compound is identified as a compound that modulates proliferation of placental stem cells. In a specific embodiment, said compound is identified as an inhibitor of differentiation. In another specific embodiment, said compound is identified as an enhancer of differentiation.

5.6.4 Placental Stem Cell Bank

Stem cells from postpartum placentas can be cultured in a number of different ways to produce a set of lots, e.g., a set of individually-administrable doses, of placental stem cells. Such lots can, for example, be obtained from stem cells from placental perfusate or from enzyme-digested placental tissue. Sets of lots of placental stem cells, obtained from a plurality of placentas, can be arranged in a bank of placental stem cells for, e.g., long-term storage. Generally, adherent stem cells are obtained from an initial culture of placental material to form a seed culture, which is expanded under controlled conditions to form populations of cells from approximately equivalent numbers of doublings. Lots are preferably derived from the tissue of a single placenta, but can be derived from the tissue of a plurality of placentas.

In one embodiment, stem cell lots are obtained as follows. Placental tissue is first disrupted, e.g., by mincing, digested with a suitable enzyme, e.g., collagenase (see Section 5.2.3, above). The placental tissue preferably comprises, e.g., the entire amnion, entire chorion, or both, from a single placenta, but can comprise only a part of either the amnion or chorion. The digested tissue is cultured, e.g., for about 1-3 weeks, preferably about 2 weeks. After removal of non-adherent cells, high-density colonies that form are collected, e.g., by trypsinization. These cells are collected and resuspended in a convenient volume of culture medium, and defined as Passage 0 cells.

Passage 0 cells are then used to seed expansion cultures. Expansion cultures can be any arrangement of separate cell culture apparatuses, e.g., a Cell Factory by NUNC™. Cells in the Passage 0 culture can be subdivided to any degree so as to seed expansion cultures with, e.g., 1×10³, 2×10³, 3×10³, 4×10³, 5×10³, 6×10³, 7×10³, 8×10³, 9×10³, 1×10⁴, 1×10⁴, 2×10⁴, 3×10⁴, 4×10⁴, 5×10⁴, 6×10⁴, 7×10⁴, 8×10⁴, 9×10⁴, or 10×10⁴ stem cells. Preferably, from about 2×10⁴ to about 3×10⁴ Passage 0 cells are used to seed each expansion culture. The number of expansion cultures can depend upon the number of Passage 0 cells, and may be greater or fewer in number depending upon the particular placenta(s) from which the stem cells are obtained.

Expansion cultures are grown until the density of cells in culture reaches a certain value, e.g., about 1×10⁵ cells/cm². Cells can either be collected and cryopreserved at this point, or passaged into new expansion cultures as described above. Cells can be passaged, e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 times prior to use. A record of the cumulative number of population doublings is preferably maintained during expansion culture(s). The cells from a Passage 0 culture can be expanded for 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38 or 40 doublings, or up to 60 doublings. Preferably, however, the number of population doublings, prior to dividing the population of cells into individual doses, is between about 15 and about 30, preferably about 20 doublings. The cells can be culture continuously throughout the expansion process, or can be frozen at one or more points during expansion.

Cells to be used for individual doses can be frozen, e.g., cryopreserved for later use. Individual doses can comprise, e.g., about 1 million to about 100 million cells per ml, and can comprise between about 10⁶ and about 10⁹ cells in total.

In a specific embodiment, of the method, Passage 0 cells are cultured for approximately 4 doublings, then frozen in a first cell bank. Cells from the first cell bank are frozen and used to seed a second cell bank, the cells of which are expanded for about another eight doublings. Cells at this stage are collected and frozen and used to seed new expansion cultures that are allowed to proceed for about eight additional doublings, bringing the cumulative number of cell doublings to about 20. Cells at the intermediate points in passaging can be frozen in units of about 100,000 to about 10 million cells per ml, preferably about 1 million cells per ml for use in subsequent expansion culture. Cells at about 20 doublings can be frozen in individual doses of between about 1 million to about 100 million cells per ml for administration or use in making a stem cell-containing composition.

In a preferred embodiment, the donor from which the placenta is obtained (e.g., the mother) is tested for at least one pathogen. If the mother tests positive for a tested pathogen, the entire lot from the placenta is discarded. Such testing can be performed at any time during production of placental stem cell lots, including before or after establishment of Passage 0 cells, or during expansion culture. Pathogens for which the presence is tested can include, without limitation, hepatitis A, hepatitis B, hepatitis C, hepatitis D, hepatitis E, human immunodeficiency virus (types I and II), cytomegalovirus, herpesvirus, and the like.

5.6.5 Treatment of Multiple Sclerosis

In another aspect, the invention provides a method of treating an individual having multiple sclerosis, or a symptom associated with multiple sclerosis, comprising administering to the individual a plurality of placental stem cells in an amount and for a time sufficient to detectably modulate, e.g., suppress an immune response in the individual.

Multiple sclerosis (MS) is a chronic, recurrent inflammatory disease of the central nervous system. The disease results in injury to the myelin sheaths surrounding CNS and PNS axons, oligodendrocytes, and the nerve cells themselves. The disease is mediated by autoreactive T cells, particularly CD4⁺ T cells, that proliferate, cross the blood-brain barrier, and enter the CNS under the influence of cellular adhesion molecules and pro-inflammatory cytokines. The symptoms of MS include sensory disturbances in the limbs, optic nerve dysfunction, pyramidal tract dysfunction, bladder dysfunction, bowel dysfunction, sexual dysfunction, ataxia, and diplopia.

Four different types or clinical courses of MS have been identified. The first, relapsing/remitting MS (RRMS) is characterized by self-limiting attacks of neurological dysfunction that manifest acutely, over the course of days to weeks, followed by a period of recovery, sometimes incomplete, over several months. The second type, secondary progressive MS (SPMS), begins as RRMS but changes such that the clinical course becomes characterized by a steady deterioration in function unrelated to acute attacks. The third, primary progressive MS (PPMS), is characterized by a steady decline in function from onset, with no acute attacks. The fourth type, progressive/relapsing MS (PRMS), also begins with a progressive course, with occasional attacks superimposed on the progressive decline in function.

Persons having MS are generally evaluated using a motor skills assessment, optionally with an MRI. For example, one motor skills assessment, the expanded disability status scale, scores gradations in an affected individual's abilities, as follows:

-   -   0.0 Normal neurological examination     -   1.0 No disability, minimal signs in one FS     -   1.5 No disability, minimal signs in more than one FS     -   2.0 Minimal disability in one FS     -   2.5 Mild disability in one FS or minimal disability in two FS     -   3.0 Moderate disability in one FS, or mild disability in three         or four FS. Fully ambulatory.     -   3.5 Fully ambulatory but with moderate disability in one FS and         more than minimal disability in several others     -   4.0 Fully ambulatory without aid, self-sufficient, up and about         some 12 hours a day despite relatively severe disability; able         to walk without aid or rest some 500 meters     -   4.5 Fully ambulatory without aid, up and about much of the day,         able to work a full day, may otherwise have some limitation of         full activity or require minimal assistance; characterized by         relatively severe disability; able to walk without aid or rest         some 300 meters.     -   5.0 Ambulatory without aid or rest for about 200 meters;         disability severe enough to impair full daily activities (work a         full day without special provisions)     -   5.5 Ambulatory without aid or rest for about 100 meters;         disability severe enough to preclude full daily activities     -   6.0 Intermittent or unilateral constant assistance (cane,         crutch, brace) required to walk about 100 meters with or without         resting     -   6.5 Constant bilateral assistance (canes, crutches, braces)         required to walk about 20 meters without resting     -   7.0 Unable to walk beyond approximately five meters even with         aid, essentially restricted to wheelchair; wheels self in         standard wheelchair and transfers alone; up and about in         wheelchair some 12 hours a day     -   7.5 Unable to take more than a few steps; restricted to         wheelchair; may need aid in transfer; wheels self but cannot         carry on in standard wheelchair a full day; May require         motorized wheelchair     -   8.0 Essentially restricted to bed or chair or perambulated in         wheelchair, but may be out of bed itself much of the day;         retains many self-care functions; generally has effective use of         arms     -   8.5 Essentially restricted to bed much of day; has some         effective use of arms retains some self care functions     -   9.0 Confined to bed; can still communicate and eat.     -   9.5 Totally helpless bed patient; unable to communicate         effectively or eat/swallow     -   10.0 Death due to MS

In the above scoring system, “FS” refers to the eight functional systems measured, including pyramidal, cerebellar, brainstem, sensory, bowel and bladder, visual, cerebral, and other systems.

Other, similar scoring systems are known, including the Scripps neurological rating scale, the ambulatory index, and the multiple sclerosis functional composite score (MSFC).

The progress of MS has also been assessed by a determination of the attack rate.

The progress of MS has also been assessed by magnetic resonance imaging, which can detect neural lesions associated with MS (e.g., new lesions, enhancing lesions, or combined unique active lesions).

Thus, in one embodiment, the invention provides a method of treating an individual having MS, e.g., and individual who has been diagnosed with MS, comprising administering to the individual a plurality of placental stem cells, wherein the placental stem cells are capable of differentiating into olidogdndrocytes, e.g., differentiate to oligodendrocytes within the individual. In a specific embodiment, the administering detectably improves one or more symptoms of MS in the individual. In more specific embodiments, the symptom is, e.g., one or more of a sensory disturbance in the limbs, an optic nerve dysfunction, a pyramidal tract dysfunction, a bladder dysfunction, a bowel dysfunction, a sexual dysfunction, ataxia, or diplopia. In another specific embodiment, said administering results in an improvement on the EDSS scale of at least one half point. In another specific embodiment, said administering results in an improvement on the EDSS scale of at least one point. In another specific embodiment, said administering results in an improvement on the EDSS scale of at least two points. In other specific embodiments, said administering results in a detectable improvement on a multiple sclerosis assessment scale or on an MRI.

MS has been treated with other therapeutic agents, for example immunomodulatory or immunosuppressive agents, e.g., interferon beta (IFNβ), including IFNβ-1a and IFN-1b; gliatriamer acetate (Copaxone); cyclophosphamide; methotrexate; azathioprine (Imuran); cladribine (Leustatin); cyclosporine; mitoxantrone; and the like. MS has also been treated with anti-inflammatory therapeutic agents, such as glucocorticoids, including adrenocorticotropic hormone (ACTH), methylprednisolone, dexamethasone, and the like. MS has also been treated with other types of therapeutic agents, such as intravenous immunoglobulin, plasma exchange, or sulfasalazine.

Thus, the invention further provides for the treatment of an individual having MS, e.g., an individual who has been diagnosed as having MS, comprising administering to the individual a plurality of placental stem cells, wherein the administering detectably improves one or more symptoms of MS in the individual, and one or more therapeutic agents, and wherein the placental stem cells are capable of differentiating into olidogdndrocytes, e.g., differentiate to oligodendrocytes within the individual. In one embodiment, the therapeutic agent is a glucocorticoid. In specific embodiments, the glucocorticoid is adrenocorticotropic hormone (ACTH), methylprednisolone, or dexamethasone. In another embodiment, the therapeutic agent is an immunomodulatory or immunosuppressive agent. In various specific embodiments, the immunomodulatory or immunosuppressive agent is IFNβ-1a, IFN-1b, gliatriamer acetate, cyclophosphamide, methotrexate, azathioprine, cladribine, cyclosporine or mitoxantrone. In other embodiments, the therapeutic agent is intravenous immunoglobulin, plasma exchange, or sulfasalazine. In another embodiment, the individual is administered any combination of the foregoing therapeutic agents.

An individual having MS, e.g., an individual diagnosed with MS, can be treated with a plurality of placental stem cells, and, optionally, one or more therapeutic agents, at any time during the progression of the disease. For example, the individual can be treated immediately after diagnosis, or within 1, 2, 3, 4, 5, 6 days of diagnosis, or within 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50 or more weeks, or 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more years after diagnosis. The individual can be treated once, or multiple times during the clinical course of the disease. The individual can be treated, as appropriate, during an acute attack, during remission, or during a chronic degenerative phase. In another embodiment, the placental stem cells are administered to a female having MS, post-partum, to maintain the state of remission or reduced occurrence of relapse experienced during pregnancy. In one embodiment, the individual is administered a dose of about 300 million placental stem cells. Dosage, however, can vary according to the individual's physical characteristics, e.g., weight, and can range from 1 million to 10 billion placental stem cells per does, preferably between 10 million and 1 billion per dose, or between 100 million and 50 million placental stem cells per dose. The administration is preferably intravenous, but can be by any art-accepted route for the administration of live cells. In one embodiment, the placental stem cells are from a cell bank.

6. EXAMPLES 6.1 Example 1 Oligodendrocyte Maintenance Medium

A representative medium for maintaining oligodendrocytes is as follows. Preferred medium is a serum-free formulation optimized for the maintenance of rodent OL lineage cells. A base media (R1236) comprises DMEM high glucose supplemented with (Sigma), 1 mM Na pyruvate, antibiotics (penicillin-streptomycin), 0.05 μg/mL insulin (to stimulate the glucose transporter), 100 μg/mL transferrin (iron uptake), 30 nM selenium (metabolic cofactor), 10 μM forskolin (cAMP), 60 μg/mL N-acetyl cystein (Redox, survival), and 5 μg/mL bovine serum albumin (carrier protein). Rodent oligodendrocyte progenitor cells are maintained using R1236 supplemented with mitogens to promote proliferation and self renewal (10 ng/mL PDGF-AA plus 5 ng/mL FGF2, or 20% v:v B104 conditioned media). To promote oligodendrocyte differentiation mitogen-containing medium is replaced with R1236 containing 10 μg/mL bovine insulin plus 5 μg/mL T3 (triiodothreonine), both of which are survival and maturation factors for rodent oligodendrocytes. All growth factors included in the medium are recombinant (human) polypeptides (R&D Inc), and the B104-cm is prepared from neuroblastoma cells (available from the ATCC) cultured at 50% confluence then exposed to R1236 for 48 hrs. This conditioned media is then filtered and aliquots stored at −30° C. until use. B104 is one of a number of neural cell lines established by Dave Schubert at the Salk Institute (Schubert et al., Nature 249:224-227 (1974)), and secretes factors that support the survival and self-renewal of rodent oligodendrocyte progenitor cells.

6.2 Example 2 Obtaining Stem Cells from Placenta by Enzymatic Digestion

An exemplary protocol for obtaining stem cells from placental tissue by enzymatic digestion is as follows. Frozen placental tissue (three pieces of approximately ˜1×1×0.5 cm each) is obtained. The tissue is umbilical cord, maternal surface of the placenta, or amniotic membrane. Digestive enzymes used include trypsin-EDTA (0.25%, GIBCO BRL); collagenase IA (Sigma), collagenase I (Worthington), collagenase 1A (Sigma)+Trypsin-EDTA, collagenase 1 (Worthington)+Trypsin-EDTA, or Elastase+Collagenase I+Collagenase IV+Daspase (Worthington). Digestion of placental tissue is as follows. Tissue is minced in the presence of enzymes (1 g in 10 ml in 50 ml tube) at 37° C., 250 rpm shaking, tube position at 45° angle for 1 hr (C25 Incubator Shaker, New Brunswick Scientific, Edison, N.J., USA). The supernatant is then discarded. The pellet is washed with 20 ml Hank's+5% FCS (3 times), and re-suspended in 12 ml culture medium. 3 ml of the resulting suspension are aliquoted into T-75 flasks containing 10 ml culture medium each (four flasks per digestion). Optionally, 10 ml Trypsin/EDTA is added for 30 min at 37° C., with shaking at 250 rpm, with recentrifugation and an additional wash with 10 ml Hank's+5% FCS. Cells are plated and cultured, selecting for adherent cells.

6.3 Example 3 Oligodendrocyte Progenitor Lineage Assays

The emergence, maturation and differentiation of OPCs can be determined by immunochemistry and transcript expression. For immunochemistry, cells growing on glass coverslips are incubated in culture media containing specific concentrations of growth factors. Coverslips removed after 1-7 days are fixed with 4% para-formaldehyde then characterized using lineage-specific antibodies (Table 1). Staining is detected using secondary antibodies coupled to fluorescent tags (Alexa Fluors, Molecular Probes Inc) and visualized by fluorescence microscopy. Secondary antibodies alone are used as a negative control. The proportion of cells that are immuno-reactive will be determined by counting up to 200 cells per coverslip. TABLE 1 Immunohistochemical reagents: Stage; Antibody Specificity Target Source Reference nSC: Nestin Ms IgG filament DSHB (Johe et al., 1996) NRP: e-NCAM Ms IgG filament DSHB GRP: A2B5 Ms IgM gangliosides cond. media (ATCC) (Eisenbarth et al., 1979) OPC: Olig2 rabbit IgG bHLH factor (H. Yakoo, JP) (Sun et al., 2001) NG2 rabbit IgG proteoglycan Chemicon (Nishiyama et al., 1996) Pdgfra goat IgG PDGF receptor R&D Inc. (Matsui et al., 1989) Unc5b goat IgG Netrin receptor R&D Inc. (Lu et al., 2004) O4 Ms IgM sulfatide CM (Bansal et al., 1989) OL: O1 Ms IgM GalC CM (Raff et al., 1978) CNPase Ms IgG myelin Sigma (Pfeiffer et al., 1993) CNPase MBP rabbit IgG myelin basic Chemicon Inc (Pfeiffer et al., 1993) neuron NF—H neurofilament Virginia Lee astrocyte GFAP rabbit IgG glial filament (Pfeiffer et al., 1993) CM = conditioned medium

Immune histochemical studies are extended by analysis of transcript expression under specific culture conditions. RNA analysis uses Northern blot (McKinnon et al., 1990) and RT-PCR (McKinnon et al., 1993b). Cells growing in 60 mm plates are recovered and RNA is harvested with TRIzol Reagent (Gibco). For RT-PCR, analysis is performed with 1 μg RNA reverse transcribed into cDNA (MoMuLV reverse transcriptase; 1:1 yield of cDNA). 50-100 ng cDNA is then used as a template for PCR amplification with Taq Polymerase and synthetic primers chosen using the Primers Selection Program as described (see. e.g., McKinnon et al., Glia 7: 245-254 (1993)). Primers are constructed to hybridize to transcripts encoding lineage-specific oligodendrocyte and oligodendrocyte precursor proteins. For new primer pairs a gradient (±10° C.) is used to establish optimal amplification parameters. PCR fragments are resolved by electrophoresis, visualized by EtBr staining, and their identity is confirmed by automated DNA sequence analysis (DNA core facility).

6.4 Example 4 Proliferation, Migration and Survival Assays

Proliferation assay: The ability of oligodendrocyte progenitors to generate a mitogenic response to specific ligands is measured in a quantitative ³H-thymidine incorporation assay. Cells are exposed to growth factors, in a dose range that brackets the maximal response to FGF and PDGF, in order to determine the half-maximal response. Responses range from a background of 500-1000 cpm (no growth factor) to 10,000 cpm (recombinant PDGF-AA), and the assay is sufficiently sensitive to accurately detect partial mitogenic responses. All cell proliferation assays are optionally performed at least three independent times. For qualitative assays, cells are exposed to mitogens with 50 μM BrdU (Sigma) present for the final 4 hrs, and DNA synthesis is monitored by dual immunofluorescence for BrdU (Osterhout et al., J. Neurosci. 17:9122-9132 (1997)) and a second lineage marker.

Proliferation assays are performed on cells that have been removed from mitogens for 24 hrs prior to exposure to recombinant growth factors to reduce background levels of DNA synthesis. The proliferation assay described herein measures the response to mitogens by increased DNA synthesis, with incorporation of ³H-thymidine during the final 4 hrs of this assay dependant on exposure to growth factors. Cells in 96 well plates (2,000 cells/well) are incubated for 24 hrs in R1236 medium lacking growth factors, then for 24 hrs in the presence of specific concentrations of factors, with 0.5 μCi/ml ³H-thymidine (Amersham) present for the final 4 hrs. Nucleic acid is recovered using an automatic harvester (Brandel) and the incorporated radioactivity measured by scintillation counting. Assays are run in triplicate (three wells) for each growth factor concentration.

Migration assay: The ability of OPCs to migrate (chemotaxis) and their directional response in response to growth factors is measured by cinematography. Quantitative assays use a modified Boyden chamber assay (Armstrong et al., 1990). In this assay, PDGF-AA mediated chemotaxis (4,000 cells/mm²) can be distinguished from background migration (1,000 cells/mm²) and from chemokinesis (random motility) by adding attractants to both upper and lower wells of the chemotaxis chamber (which abolishes chemotaxis but not chemokinesis) (see Armstrong et al., J. Neurosci. Res. 27:400-407 (1990)).

Cells are cultured for 16 hrs in media lacking mitogens then transferred into the top wells of a microchemotaxis chamber (20,000 cells/well) in defined medium, with a polycarbonate filter separating them from the lower chamber containing media plus attractant. Growth factors are given in triplicate wells for each concentration, and the cells are incubated for 16 hrs at 37° C. The number of cells migrated per mm² on the lower side of the filter is determined by counting GFP-tagged cells, and total migration is determined after staining the membrane with Dip-Quik (American Scientific).

Survival assays: The survival of individual OPCs is measured using the MTT assay, (Mosmann, 1983) and chromatin fragmentation (nucleosome laddering) using a modified TUNEL assay (Gavrieli et al., J. Cell. Biol. 119:493-501 (1992)) as described (Yasuda et al., J. Neurosci. Res. 40:306-317 (1995)). Cells are cultured for 24 hrs in media containing bFGF, PDGF-AA, or without growth factors, and the number of cells which incorporate MTT, or the level of nick end labeling, are compared between mutant and wild type OL cultures. The PI3K inhibitor wortmannin is used as a positive control for cell death (Ebner et al., J. Neurosci. Res. 62:336-345 (2000)).

The MTT assay is performed on cells growing in 96 well plates, and the proportion of labeled cells will be determined by counting stained cells as previously described (Barres et al., Cell 70:31-46 (1992)) The ability of bFGF and PDGF-AA to prevent DNA fragmentation is determined by analysis of chromatin DNA from cells growing in the presence or absence of increasing concentrations of these factors. For quantitative analysis, cells growing in 96 well plates are incubated in PBS containing 4 units terminal transferase (Promega Biotech.), 2 μCi [α-³²P]-dideoxyATP (Amersham), and 0.3% Triton X-100 for 60 min at 37° C., then the cell lysates are harvested on Whatman GF/C filters (Brandel Cell Harvester) and ³²P-incorporation into 3′-ends of DNA is determined by liquid scintillation counting. The assay is enzyme dependent and gives a background of 10,000 cpm and incorporation of 100,000 cpm in cells cultured for 72 hrs in the presence of 1 μM staurosporine (Ebner, 2000) For qualitative analysis of nucleosome laddering, DNA is isolated from cells growing in 35 mm dishes, end labeled with terminal transferase and ³²P-ddATP in vitro, size separated on agarose gels to resolve nucleosome-sized fragments, and the incorporation of radioactivity is determined by densitometry.

6.5 Example 5 Flow Cytometry

To perform intracellular staining for flow cytometry, approximately 5×10⁵ PDSCs are permeabilized with 0.5 mL of Beckman Coulter IntraPrep reagent for 15 minutes. After rinsing with PBS, cells are incubated with primary antibody (1 g) on ice for 30 minutes followed by two washes. Cells are resuspended in a 1:100 of secondary antibody and incubated for 30 minutes. After staining, cells are washed twice and analyzed immediately on a BeckmanCoulter XL-MCL flow cytometer. To evaluate protein expression in untreated and IBMX-induced cells, 1.5×10×10⁴ cells are collected using FL1 (FITC) and FL2 (CY3) signals. Dead cells and debris are eliminated by using a high forward and orthogonal light scatter window or by propidium iodine (PI) exclusion.

Mouse, rabbit, and donkey primary antibodies and final dilutions are as follows: rabbit anti-nestin, 1:100 (BD PharMingen); mouse anti-neuron specific enolase, 1:100 (Chemicon); mouse anti-myelin/oligodendrocyte specific protein, 1:100 (DAKO); mouse anti-neurofilament-L, 1:100 (DAKO); rabbit anti-glial fibrillary acidic protein, 1:200 (DAKO); mouse anti-vimentin, 1:100 (BD PharMingen). The following antibodies, which are used in flow cytometry experiments, are available from Becton Dickinson and are used at a 1:10 dilution:anti-CD45, anti-CD34, anti-CD29, anti-CD10, anti-HLA-1, anti-CD54, anti-CD90, anti-SH2, and anti-SH3.

Cells are incubated in DMEM containing 10% FCS on polyornithine-coated glass coverslips (Sigma). Cells are fixed with 4% paraformaldehyde in PBS for 10 minutes and permeabilized for 10 minutes with 0.2% Triton X-100 in PBS at RT. Cells are then incubated with the primary antibody for 30 minutes at 37° C. Following three washes with PBS, cells are incubated with either fluorescein (FITC)-conjugated donkey anti-mouse IgG (Jackson Laboratories) or Cy3-conjugated goat anti-rabbit IgG (Jackson Laboratories), both at a 1:50 dilution for 30 minutes at 37° C. in the dark. Labeled cells are washed and mounted with Vectashield mounting medium (Vector Laboratories). 

1. A method of producing an oligodendrocyte, comprising culturing a placenta-derived stem cell under conditions and for a time sufficient for said stem cell to exhibit a characteristic of an oligodendrocyte.
 2. The method of claim 1, wherein said characteristic is the production of myelin oligodendrocyte specific protein or expression of a gene encoding myelin oligodendrocyte specific protein.
 3. The method of claim 1, wherein said culturing comprises contacting said stem cell with isobutylmethylxanthine (IBMX).
 4. An oligodendrocyte produced by the method of claim
 1. 5. A method of treating a subject having a disease, disorder or condition associated with abnormal myelination, comprising introducing the oligodendrocyte of claim 4 to said subject.
 6. The method of claim 5, wherein said disease, disorder or condition is multiple sclerosis. 